SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* Trident III, L.P. (Last) (First) (Middle) WALKERS CORPORATE SERVICES LIMITED WALKER HOUSE, 87 MARY STREET (Street) GEORGE TOWN, GRAND CAYMAN E9 KY1-9002 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 05/12/2010	3. Issuer Name and Ticker or Trading Symbol ALTERRA CAPITAL HOLDINGS Ltd [ ALTE ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Shares	8,264,544(1)	D
Common Shares	201,131(2)	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Warrants (right to buy)	(3)	12/15/2015	Common Shares	4,123,825(4)	$22.54	D
Warrants (right to buy)	(3)	12/15/2015	Common Shares	100,022(5)	$22.54	D

1. Name and Address of Reporting Person* Trident III, L.P. (Last) (First) (Middle) WALKERS CORPORATE SERVICES LIMITED WALKER HOUSE, 87 MARY STREET (Street) GEORGE TOWN, GRAND CAYMAN E9 KY1-9002 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Trident III Professionals fund L P (Last) (First) (Middle) WALKERS CORPORATE SERVICES LIMITED WALKER HOUSE, 87 MARY STREET (Street) GEORGE TOWN, GRAND CAYMAN E9 KY1-9002 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Trident Capital III, L.P. (Last) (First) (Middle) WALKERS CORPORATE SERVICES LIMITED WALKER HOUSE, 87 MARY STREET (Street) GEORGE TOWN, GRAND CAYMAN E9 KY1-9002 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Stone Point GP Ltd. (Last) (First) (Middle) WALKERS CORPORATE SERVICES LIMITED WALKER HOUSE, 87 MARY STREET (Street) GEORGE TOWN, GRAND CAYMAN E9 KY1-9002 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* STONE POINT CAPITAL LLC (Last) (First) (Middle) 20 HORSENECK LANE (Street) GREENWICH CT 06830 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. Represents shares owned of record by Trident III, L.P. ("Trident III"). Trident Capital III, L.P. ("Trident GP") is the sole general partner of Trident III. The general partners of Trident GP are four single member limited liability companies that are owned by individuals who are members of Stone Point Capital LLC ("Stone Point"), which serves as the investment manager of Trident III and Trident III PF (as defined below). Each of the single member limited liability companies that acts as a general partner of Trident GP disclaims beneficial ownership of shares of Alterra Capital Holdings Limited ("Alterra") that are, or may be deemed to be, beneficially owned by Trident III, other than shares in which they may be deemed to have a pecuniary interest. Trident III disclaims beneficial ownership of shares that are, or may be deemed to be, beneficially owned by Trident III PF.

2. Represents shares owned of record by Trident III Professionals Fund, L.P. ("Trident III PF"). Stone Point GP Ltd. ("Trident PF GP"), a company owned by certain individuals who are members of Stone Point, is the sole general partner of Trident III PF. Trident III PF disclaims beneficial ownership of shares that are, or may be deemed to be, beneficially owned by Trident III.

3. All warrants are immediately exercisable.

4. These warrants are owned of record by Trident III.

5. These warrants are owned of record by Trident III PF.

Remarks:

In its role as manager of Trident III and Trident III PF, Stone Point has authority delegated to it by Trident GP and Trident PF GP to exercise voting rights with respect to securities of Alterra that are held by Trident III and Trident III PF, respectively, but does not have any power with respect to the disposition of any such Alterra securities that are held by Trident III or Trident III PF. Stone Point disclaims beneficial ownership of all such Alterra securities, except to the extent of any pecuniary interest therein. In addition, each Common Share of Alterra entitles its holder to one vote on each matter that is voted upon by poll at a general meeting of Alterra, subject to certain provisions of Alterra's bye-laws that reduce the total voting power of any U.S. shareholder owning, directly or indirectly, beneficially or otherwise, as described in Alterra's bye-laws, 9.5% or more of the Common Shares to less than 9.5% of the total voting power of Common Shares.

	By: Stone Point Capital LLC, as manager; /s/ David Wermuth, Principal	05/19/2010
	By: Stone Point Capital LLC, as manager; /s/ David Wermuth, Principal	05/19/2010
	By: DW Trident GP, LLC, a general partner; /s/ David Wermuth, Sole Member	05/19/2010
	/s/ David Wermuth, Director	05/19/2010
	/s/ David Wermuth, Principal	05/19/2010
	** Signature of Reporting Person	Date
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