CUSIP No.  US0042251084

13G

Page 1 of 17 Pages

UNITED STATES

OMB APPROVAL

SECURITIES AND EXCHANGE COMMISSION

OMB Number:
3235-0145

Washington, D.C. 20549

Expires:
December 31, 2005

SCHEDULE 13G

Estimated average burden hours per response. . 11

o

Rule 13d-1(b)

o

Rule 13d-1(c)

ý

Rule 13d-1(d)

CUSIP No.  US0042251084

13G

Page 2 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Oxford Bioscience Partners IV L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815 shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815  shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
PN

CUSIP No.  US0042251084

13G

Page 3 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
mRNA Fund II L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
PN

CUSIP No.  US0042251084

13G

Page 4 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
OBP Management IV L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
PN

CUSIP No.  US0042251084

13G

Page 5 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Jeffrey T. Barnes

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No.  US0042251084

13G

Page 6 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Mark P. Carthy

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No.  US0042251084

13G

Page 7 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Jonathan J. Fleming

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No.  US0042251084

13G

Page 8 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Michael E. Lytton

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
0 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.41%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No.  US0042251084

13G

Page 9 of 17 Pages

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Alan G. Walton

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
9,000 shares

6.

Shared Voting Power 
2,599,815  shares

7.

Sole Dispositive Power 
9,000 shares

8.

Shared Dispositive Power
2,599,815 shares

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,599,815  shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
15.46%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No.  US0042251084

13G

Page 10 of 17 Pages

Item 1.

(a)

Name of Issuer
Acadia Pharmaceuticals Inc.

(b)

Address of Issuer’s Principal Executive Offices
3911 Sorrento Valley Boulevard, San Diego, California, 92121

Item 2.

Item 2(a)

Item 2(b)

Item 2(c)

Name of Person Filing

Address

Citizenship or
Place of Organization

Oxford Bioscience Partners IV L.P. (“Oxford IV”)

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

Delaware

mRNA Fund II L.P. (“mRNA II”)

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

Delaware

OBP Management IV L.P. (“OBP IV”), the general partner of Oxford IV and mRNA II

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

Delaware

Jeffrey T. Barnes, a general partner of OBP IV

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

United States

Mark P. Carthy, a general partner of OBP IV

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

United States

Jonathan J. Fleming, a general partner of OBP IV

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

United States

Michael E. Lytton, a general partner of OBP IV

Oxford Bioscience Partners
222 Berkeley St.
Boston, MA 02116

United States

Alan G. Walton, a general partner of OBP IV

Oxford Bioscience Partners
315 Post Rd. West
Westport, CT 06880

United States

CUSIP No.  US0042251084

13G

Page 11 of 17 Pages

(d)

Title of Class of Securities
Common Stock, $0.0001 par value.

(e)

CUSIP Number
US0042251084

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

o

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Not applicable.

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   

As of December 31, 2004 each of the following is the owner of record of the number of shares of Common Stock, $0.0001 of Acadia Pharmaceuticals Inc. set forth next to his or its name:

Oxford IV:

2,573,836 Shares

mRNA II:

25,979 Shares

OBP IV:

0 Shares

Mr. Barnes:

0 Shares

Mr. Carthy:

0 Shares

Mr. Fleming:

0 Shares

Mr. Lytton:

0 Shares

Mr. Walton:

9,000 Shares

By virtue of their relationship as affiliated limited partnerships, whose sole general partner shares individual general partners, Oxford IV and mRNA II may be deemed to share voting power and the power to direct the disposition of the shares which each partnership owns of record.  OBP IV (as the general partner of Oxford IV and mRNA II), may also be deemed to own beneficially the shares held of record by Oxford IV and mRNA II.  Each of Messrs. Barnes, Carthy, Fleming, Lytton, and Walton, the individual general partners of OBP IV, may be deemed to own beneficially the shares held by Oxford IV and mRNA II.  Note that 9,000 of the beneficially owned shares of Walton consist of shares issuable upon the exercise of options to purchase shares, which are immediately exercisable.

CUSIP No.  US0042251084

13G

Page 12 of 17 Pages

(b)

Percent of class:   

Oxford IV:

15.41%

mRNA II:

15.41%

OBP IV:

15.41%

Mr. Barnes:

15.41%

Mr. Carthy:

15.41%

Mr. Fleming:

15.41%

Mr. Lytton:

15.41%

Mr. Walton:

15.46%

The foregoing percentages are calculated based on the 16,866,979 shares of Common Stock reported to be outstanding as of October 31, 2004 in the Quarterly Report on Form 10-Q of Acadia Pharmaceuticals Inc. for the quarter ended September 30, 2004 (as adjusted pursuant to Rule 13d-3(d)(1)).

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote  

Oxford IV:

0 Shares

mRNA II:

0 Shares

OBP IV:

0 Shares

Mr. Barnes:

0 Shares

Mr. Carthy:

0 Shares

Mr. Fleming:

0 Shares

Mr. Lytton:

0 Shares

Mr. Walton:

9,000 Shares

(ii)

Shared power to vote or to direct the vote    

Oxford IV:

2,599,815 Shares

mRNA II:

2,599,815 Shares

OBP IV:

2,599,815 Shares

Mr. Barnes:

2,599,815 Shares

Mr. Carthy:

2,599,815 Shares

Mr. Fleming:

2,599,815 Shares

Mr. Lytton:

2,599,815 Shares

Mr. Walton:

2,599,815 Shares

CUSIP No.  US0042251084

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Page 13 of 17 Pages

(iii)

Sole power to dispose or to direct the disposition of   

Oxford IV:

0 Shares

mRNA II:

0 Shares

OBP IV:

0 Shares

Mr. Barnes:

0 Shares

Mr. Carthy:

0 Shares

Mr. Fleming:

0 Shares

Mr. Lytton:

0 Shares

Mr. Walton:

9,000 Shares

(iv)

Shared power to dispose or to direct the disposition of   

Oxford IV:

2,599,815 Shares

mRNA II:

2,599,815 Shares

OBP IV:

2,599,815 Shares

Mr. Barnes:

2,599,815 Shares

Mr. Carthy:

2,599,815 Shares

Mr. Fleming:

2,599,815 Shares

Mr. Lytton:

2,599,815 Shares

Mr. Walton:

2,599,815 Shares

Each of Oxford IV, mRNA II, OBP IV, and Messrs. Barnes, Carthy, Fleming, Lytton and Walton expressly disclaims beneficial ownership of any shares of the Common Stock of Acadia Pharmaceuticals Inc., except to the extent of his or its pecuniary interest therein and any shares held directly of record.

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   o.

Not applicable.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not applicable.

Item 8.

Identification and Classification of Members of the Group

Not applicable.  Oxford IV, mRNA II, OBP IV, Messrs. Barnes, Carthy, Fleming, Lytton and Walton expressly disclaim membership in a “group” as used in Rule 13d 1(b)(ii)(J) of the Act.

Item 9.

Notice of Dissolution of Group

Not applicable.

CUSIP No.  US0042251084

13G

Page 14 of 17 Pages

Item 10.

Certification

By signing below each of Oxford IV, mRNA II, OBP IV, and Messrs. Barnes, Carthy, Fleming, Lytton and Walton certify that, to the best of its or his knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

CUSIP No.  US0042251084

13G

Page 15 of 17 Pages

Dated:  February 14, 2005

OXFORD BIOSCIENCE PARTNERS IV L.P.

By:  OBP Management IV L.P., its general partner

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

MRNA FUND II L.P.

By:  OBP Management IV L.P., its general partner

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

OBP MANAGEMENT IV L.P.

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

/s/ Jeffrey T. Barnes

Jeffrey T. Barnes

/s/ Mark P. Carthy

Mark P. Carthy

/s/ Jonathan J. Fleming

Jonathan J. Fleming

/s/ Michael E. Lytton

Michael E. Lytton

/s/ Alan G. Walton

Alan G. Walton

CUSIP No.  US0042251084

13G

Page 16 of 17 Pages

Dated:  February 14, 2005

OXFORD BIOSCIENCE PARTNERS IV L.P.

By:  OBP Management IV L.P., its general partner

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

MRNA FUND II L.P.

By:  OBP Management IV L.P., its general partner

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

OBP MANAGEMENT IV L.P.

By:

/s/ Jonathan J. Fleming

Jonathan J. Fleming

General Partner

/s/ Jeffrey T. Barnes

Jeffrey T. Barnes

/s/ Mark P. Carthy

Mark P. Carthy

/s/ Jonathan J. Fleming

Jonathan J. Fleming

/s/ Michael E. Lytton

Michael E. Lytton

/s/ Alan G. Walton

Alan G. Walton

CUSIP No.  US0042251084

13G

Page 17 of 17 Pages