| Item 1. | |
| (a) | Name of issuer:
GENERATION BIO CO. |
| (b) | Address of issuer's principal executive offices:
301 BINNEY STREET, CAMBRIDGE, MA, 02142. |
| Item 2. | |
| (a) | Name of person filing:
This Schedule 13G is filed by (i) Atlas Venture Fund X, L.P., a Delaware limited partnership ("Atlas X"), (ii) Atlas Venture Associates X, L.P., a Delaware limited partnership ("AVA X LP"), (iii) Atlas Venture Associates X, LLC, a Delaware limited liability company ("AVA X LLC" and together with Atlas X and AVA X LP, the "Fund X Reporting Persons"), (iv) Atlas Venture Opportunity Fund I, L.P., a Delaware limited partnership ("AVO I"), (v) Atlas Venture Associates Opportunity I, L.P., a Delaware limited partnership ("AVAO LP") and (vi) Atlas Venture Associates Opportunity I, LLC, a Delaware limited liability company ("AVAO LLC" and together with AVO I and AVAO LP, the "Opportunity Fund Reporting Persons" and together with the Fund X Reporting Persons, the "Reporting Persons"). |
| (b) | Address or principal business office or, if none, residence:
300 Technology Square, 8th Floor
Cambridge, Massachusetts 02139 |
| (c) | Citizenship:
Each of Atlas X, AVA X LP, AVO I and AVAO LP is a Delaware limited partnership. Each of AVA X LLC and AVAO LLC is a Delaware limited liability company. |
| (d) | Title of class of securities:
COMMON STOCK, $0.0001 PAR VALUE |
| (e) | CUSIP No.:
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| 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) |  Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
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| (b) | Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
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| (c) | Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
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| (d) | Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
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| (e) | An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
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| (f) | An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
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| (g) | A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
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| (h) | A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
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| (i) | 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);
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| (j) | A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
|
| (k) | Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
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| | |
| Item 4. | Ownership |
| (a) | Amount beneficially owned:
0 |
| (b) | Percent of class:
0 %
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| (c) | Number of shares as to which the person has:
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| | (i) Sole power to vote or to direct the vote:
0
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| | (ii) Shared power to vote or to direct the vote:
0
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| | (iii) Sole power to dispose or to direct the disposition of:
0
|
| | (iv) Shared power to dispose or to direct the disposition of:
0
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| Item 5. | Ownership of 5 Percent or Less of a Class. |
| | 
Ownership of 5 percent or less of a class
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| Item 6. | Ownership of more than 5 Percent on Behalf of Another Person. |
| |
Not Applicable
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| Item 7. | Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person. |
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Not Applicable
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| Item 8. | Identification and Classification of Members of the Group. |
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Not Applicable
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| Item 9. | Notice of Dissolution of Group. |
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Not Applicable
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