UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                 SCHEDULE 13D/A

                    Under the Securities Exchange Act of 1934
                               (Amendment No. 7)*

                             3D Systems Corporation
                             ----------------------
                                (Name of Issuer)

                     Common Stock, par value $.001 per share
                     ---------------------------------------
                         (Title of Class of Securities)

                                    88554D205
                                 --------------
                                 (CUSIP Number)

                                 Kevin S. Moore
                                    President
                             The Clark Estates, Inc.
                        One Rockefeller Plaza, 31st Floor
                            New York, New York 10020
                                 (212) 977-6900
            --------------------------------------------------------
            (Name, Address and Telephone Number of Person Authorized
                     to Receive Notices and Communications)

                                    Copy to:

                            Jeffrey E. LaGueux, Esq.
                       Patterson Belknap Webb & Tyler LLP
                           1133 Avenue of the Americas
                          New York, New York 10036-6710
                                 (212) 336-2000

                                December 31, 2007
             -------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
Schedule because of ss.ss.240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the
following box. |_|

Note: Schedules filed in paper format shall include a signed original and five
copies of the Schedule, including all exhibits. See Rule 13d-7 for other parties
to whom copies are sent.

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).


                               (Page 1 of 3 pages)


CUSIP No. 88554D205                    13D
--------------------------------------------------------------------------------
1     NAME OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

      The Clark Estates, Inc.
      13-5524538
--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                   (a) |_|
                                                                         (b) |X|

--------------------------------------------------------------------------------
3     SEC USE ONLY


--------------------------------------------------------------------------------
4     SOURCE OF FUNDS

      OO
--------------------------------------------------------------------------------
5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
      PURSUANT TO ITEMS 2(d) OR 2(e)                                         |_|


--------------------------------------------------------------------------------
6     CITIZENSHIP OR PLACE OF ORGANIZATION

      New York
--------------------------------------------------------------------------------
               7     SOLE VOTING POWER

                     2,223,157
               -----------------------------------------------------------------
  NUMBER OF    8     SHARED VOTING POWER
   SHARES
 BENEFICIALLY        0
  OWNED BY     -----------------------------------------------------------------
    EACH       9     SOLE DISPOSITIVE POWER
  REPORTING
   PERSON            2,223,157
    WITH       -----------------------------------------------------------------
               10    SHARED DISPOSITIVE POWER

                     0
--------------------------------------------------------------------------------
11    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      2,223,157
--------------------------------------------------------------------------------
12    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES  |_|


--------------------------------------------------------------------------------
13    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

      10.03%
--------------------------------------------------------------------------------
14    TYPE OF REPORTING PERSON

      CO
--------------------------------------------------------------------------------


                               (Page 2 of 3 pages)


                                 AMENDMENT NO. 7
                                       TO
                                  SCHEDULE 13D


      This Amendment No. 7 is filed in accordance with Rule 13d-2 of the
Securities Exchange Act of 1934, as amended, by the Reporting Person and refers
only to information which has materially changed since the filing of Amendment
No. 6 to Schedule 13D by the Reporting Person on September 19, 2006. The items
identified below, or the particular paragraphs of such items which are
identified below, are amended to add the information as set forth below.
Capitalized terms not otherwise defined herein have the meanings ascribed to
them in the original Schedule 13D or the amendments thereto.

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER

      (a) The 2,223,157 shares of Common Stock beneficially owned by the
Reporting Person as of December 31, 2007 constitute approximately 10.03% of the
outstanding shares of Common Stock, computed in accordance with the provisions
of SEC Rule 13d-3(d)(1) (based upon an aggregate of 22,155,323 outstanding
shares of Common Stock as disclosed in the Issuer's Quarterly Report on Form
10-Q for the quarter ended September 30, 2007.

      (c) On July 20, 2007, the Reporting person converted the Debenture
described in the prior Schedule 13D filings into an aggregate of 294,696 shares
of Common Stock pursuant to the conversion terms of such Debenture. The
aggregate number of shares of Common Stock of the Company beneficially owned by
the Reporting Person did not change as a result of this conversion, however,
because these shares were deemed beneficially owned by the Reporting Person
prior to the conversion of the Debenture in accordance with SEC Rule 13d-3(d)..

                                    Signature

      After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Date:  February 13, 2008                             THE CLARK ESTATES, INC.


                                                     By: /s/ Kevin S. Moore
                                                         -----------------------
                                                         Name:  Kevin S. Moore
                                                         Title: President


                               (Page 3 of 3 pages)