UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

o

Rule 13d-1(b)

o

Rule 13d-1(c)

ý

Rule 13d-1(d)

CUSIP No. 252131 10 7

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
The St. Paul Travelers Companies, Inc.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

Not Applicable

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Minnesota corporation

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
3,828,062 (see Item 4)

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,828,062 (see Item 4)

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,828,062 (see Item 4)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable.

11.

Percent of Class Represented by Amount in Row (9)
15.1%

12.

Type of Reporting Person (See Instructions)
HC, IC and CO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
St. Paul Fire and Marine Insurance Company

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

Not Applicable

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Minnesota corporation

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
3,828,062 (see Item 4)

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,828,062 (see Item 4)

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,828,062 (see Item 4)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable.

11.

Percent of Class Represented by Amount in Row (9)
15.1%

12.

Type of Reporting Person (See Instructions)
IC and CO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Split Rock Partners, LLC

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

Not Applicable

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware Limited Liability company

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
3,853,510 (see Item 4)

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,853,510 (see Item 4)

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,853,510 (see Item 4)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable.

11.

Percent of Class Represented by Amount in Row (9)
15.2%

12.

Type of Reporting Person (See Instructions)
OO

Item 1.

(a)

Name of Issuer
The name of the issuer is Dexcom, Inc. (the “Issuer”).

(b)

Address of Issuer’s Principal Executive Offices
The address of the principal executive offices of the Issuer is 5555 Oberlin Drive, San Diego, CA 92121.

Item 2.

(a)

Name of Person Filing
The St. Paul Travelers Companies, Inc. (“The St. Paul”), St. Paul Fire and Marine Insurance Company (“F&M”) and Split Rock Partners, LLC (“Split Rock”).  The St. Paul, F&M and Split Rock are collectively referred to herein as the “Reporting Persons.”

(b)

Address of Principal Business Office or, if none, Residence
The principal business address of each of The St. Paul and F&M is 385 Washington Street, St. Paul, Minnesota  55102.  The principal business address of Split Rock is 10400 Viking Drive, Suite 550, Eden Prairie, MN 55344.

(c)

Citizenship
Each of The St. Paul and F&M is a Minnesota corporation.  Split Rock is a Delaware limited liability company.

(d)

Title of Class of Securities
The class of equity securities to which this Statement relates is the common stock, par value $0.001 per share, of the Issuer (the “Common Stock”).

(e)

CUSIP Number
The CUSIP number of the Common Stock is 252131 10 7.

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)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

o

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

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);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)           Amount beneficially owned:     The St. Paul and F&M may be deemed to own beneficially 3,828,062 shares of Common Stock of the Issuer, and Split Rock may be deemed to own beneficially 3,853,510 shares of Common Stock of the Issuer.  F&M is a wholly owned subsidiary of The St. Paul.  F&M owns a controlling interest of St. Paul Venture Capital V, LLC (“SPVC V”) and St. Paul Venture Capital VI, LLC (“SPVC VI”, and collectively with SPVC V, the “SPVC Funds”), Fog City Fund, LLC (“Fog City”), Windamere, LLC (“Windamere”), Windamere II, LLC (“Windamere II”) and Windamere III, LLC (“Windamere III”, and collectively with Windamere, Windamere II and Fog City, the “Satellite Funds”).   The SPVC Funds and St. Paul Venture Capital Affiliates Fund I, LLC (“SPVC Affiliates”) are jointly managed by Split Rock and Vesbridge Partners, LLC, however, voting and investment power over the shares has been delegated solely to Split Rock.  Voting and investment power with respect to the shares has been delegated by Split Rock to four individuals, who require a two-thirds vote to act.  The Satellite Funds are managed by the managing member of each individual Satellite Fund, however, investments or dispositions in excess of certain amounts must be approved by the board of directors of each Satellite Fund.  Split Rock has the right to appoint a majority of the members of the board of directors of each Satellite Fund.  The table below sets forth the securities held by each entity described herein:

Entity

Common Shares

SPVC V

1,343,272

SPVC VI

674,301

SPVC Affiliates

25,448

Fog City

937,653

Windamere

308,375

Windamere II

385,688

Windamere III

178,773

By virtue of the affiliate relationships among The St. Paul, F&M, the SPVC Funds and the Satellite Funds, The St. Paul and F&M may each be deemed to own beneficially 3,828,062 shares described in this Schedule 13G. By virtue of the affiliate relationships among The St. Paul, F&M, Split Rock, the SPVC Funds, SPVC Affiliates and the Satellite Funds, Split Rock may be deemed to own beneficially 3,853,510 shares described in this Schedule 13G.

The filing of this Statement shall not be construed as an admission that The St. Paul, F&M or Split Rock is the beneficial owner of any securities covered by this Statement

(b)           Percent of class:The St. Paul & F&M: 15.1%, and Split Rock: 15.2%. The foregoing percentages are calculated based on the 25,378,213 shares of Common Stock represented to be outstanding by the Issuer on its most recently filed quarterly report on Form 10-Q for the quarter ended September 30, 2005.

(c)

Number of shares as to which the person has:

The St. Paul and F&M

(i)

Sole power to vote or to direct the vote

0

(ii)

Shared power to vote or to direct the vote

3,828,062

(iii)

Sole power to dispose or to direct the disposition of

0

(iv)

Shared power to dispose or to direct the disposition of

3,828,062

Number of shares as to which the person has:

Split Rock

(i)

Sole power to vote or to direct the vote

0

(ii)

Shared power to vote or to direct the vote

3,853,510

(iii)

Sole power to dispose or to direct the disposition of

0

(iv)

Shared power to dispose or to direct the disposition of

3,853,510

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the followingo.

Not Applicable.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not Applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not Applicable.

Item 8.

Identification and Classification of Members of the Group

Not Applicable.

Item 9.

Notice of Dissolution of Group

Not Applicable.

Item 10.

Certification

By signing below, each of the undersigned below certifies that, to the best of its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the Issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Date: February 8, 2006.

THE ST. PAUL TRAVELERS COMPANIES, INC.

By:

/s/ Bruce A. Backberg

Bruce A. Backberg

Its:

Senior Vice President

ST. PAUL FIRE AND MARINE INSURANCE COMPANY

By:

/s/ Bruce A. Backberg

Bruce A. Backberg

Its:

Senior Vice President

SPLIT ROCK PARTNERS, LLC

By:

/s/ Steven L.P. Schwen

Steven L.P. Schwen

Its:

Chief Financial Officer

Dated: February 8, 2006.

THE ST. PAUL TRAVELERS COMPANIES, INC.

By:

/s/ Bruce A. Backberg

Bruce A. Backberg

Its:

Senior Vice President

ST. PAUL FIRE AND MARINE INSURANCE COMPANY

By:

/s/ Bruce A. Backberg

Bruce A. Backberg

Its:

Senior Vice President

SPLIT ROCK PARTNERS, LLC

By:

/s/ Steven L.P. Schwen

Steven L.P. Schwen

Its:

Chief Financial Officer