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* Flagship Ventures Fund 2004 L P (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 12/06/2017	3. Issuer Name and Ticker or Trading Symbol Quanterix Corp [ QTRX ]
		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)

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
Series A-1 Preferred Stock	(1)	(2)	Common Stock	398,257	(3)	D(4)
Series A-2 Preferred Stock	(1)	(2)	Common Stock	1,045,426	(3)	D(4)
Series B Preferred Stock	(1)	(2)	Common Stock	477,042	(3)	D(4)
Series C Preferred Stock	(1)	(2)	Common Stock	109,770	(3)	D(4)

1. Name and Address of Reporting Person* Flagship Ventures Fund 2004 L P (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* Flagship Ventures General Partner LLC (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* AFEYAN NOUBAR (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* KANIA EDWIN M JR (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

Explanation of Responses:

1. These shares are convertible into the Issuer's common stock in accordance with the Issuer's Restated Certificate of Incorporation, as amended, at any time after the issuance of such shares, at the holder's election.

2. Not applicable.

3. The shares of preferred stock will convert into common stock immediately prior to the closing of the Issuer's initial public offering using a calculation defined in the Issuer's Restated Certificate of Incorporation, as amended, based on the initial purchase price and the conversion rate in effect at the time of conversion. The shares of preferred stock will convert on a 1-for-3.214 basis and such conversion rate is reflected in the amount of common stock underlying the security.

4. Held by Flagship Ventures Fund 2004, L.P. Flagship Ventures General Partner LLC (the "GP") is the General Partner of Flagship Ventures Fund 2004, L.P. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the Managers of the GP. The GP, Dr. Afeyan and Mr. Kania may be deemed to possess voting and investment control over all shares held by Flagship Ventures Fund 2004, L.P. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

	FLAGSHIP VENTURES FUND 2004, L.P. By: Flagship Ventures General Partner LLC By: /s/ Noubar B. Afeyan, Ph.D., Manager	12/06/2017
	FLAGSHIP VENTURES GENERAL PARTNER LLC By: /s/ Noubar B. Afeyan, Ph.D., Manager	12/06/2017
	/s/ Noubar B. Afeyan, Ph.D.	12/06/2017
	/s/ Edwin M. Kania, Jr.	12/06/2017
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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