13G Filing: James E. Flynn and Marinus Pharmaceuticals Inc (MRNS)

Marinus Pharmaceuticals, Inc.

170 N. Radnor Chester Road, Suite 250

Radnor, Pennsylvania 19087

James
E. Flynn, Deerfield Mgmt, L.P., Deerfield Special Situations Fund, L.P., and Deerfield Management Company, L.P.

James E. Flynn, Deerfield Mgmt, L.P., Deerfield
Special Situations Fund, L.P. and Deerfield Management Company, L.P., 780 Third Avenue, 37th Floor, New York, NY 10017

Deerfield
Mgmt, L.P., Deerfield Management Company, L.P. and Deerfield Special Situations Fund, L.P. – Delaware limited partnerships;

James E. Flynn – United States citizen

common
stock, par value $0.001

56854Q101

If This Statement is Filed Pursuant to
Rule 13d-1(b), or 13d-2(b) or (c), Check Whether the Person Filing is a:

Broker or dealer registered under Section 15 of the
Exchange Act.

Insurance company as defined in Section 3(a)(19) of
the Exchange Act.

Investment company registered under Section 8 of the
Investment Company Act.

An employee benefit plan or endowment fund in accordance
with Rule 13d-1(b)(1)(ii)(F);

A parent holding company or control person in accordance
with Rule 13d-1(b)(1)(ii)(G);

(h)

A savings association as defined in Section 3(b) of
the Federal Deposit Insurance Act;

A church plan that is excluded from the definition
of an investment company under Section 3(c)(14) of the Investment Company Act;