Vol. XXI, pp 211-212 December 10, 1908 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



A NEW SHIPWORM FROM THE UNITED STATES. 



BY PAUL BARTSCH, 



Assistant Curator Division of Mollusks, V. S. Natl. Mis. 



In revising the collection of American shipworms in the U. S. 

 National Museum, I find that the commonest one of the East 

 Coast species is an undescribed form which has been variously 

 referred to Xylotrya palmvlata, bipalmidata, bipinnata and fim- 

 briate . It may be known as 



Xylotrya gouldi sp. nov. 



Exterior. — Shell subglobose, milk white. The shell is divided into three 

 parts, an anterior and posterior projection and a main or central part. 

 Anterior projection not quite as high as the umbo, large ami expanded, 

 differentiated from the central part of the shell by a well-marked constric- 

 tion. Posterior notch forming an angle a little greater than a right angle. 

 The posterior projection is marked by a series of parallel, eqnal and 

 equally spaced, subtriangular and subacute, exceedingly finely denticulate 

 ridges which are about three-quarters as wide at their base as the flat 

 spaces that separate them. There are nine (9) of these ridges in the space 

 of one millimeter at the junction of the posterior projection with the 

 central part of the shell. The central part of the shell is divided into 

 three parts. An anterior, well-rounded, smooth portion, which is marked 

 by lines of growth only; a median centrally moderately depressed area, 

 which is marked by strong lines of growth on the anterior half, and 

 very strong, irregular, raised, rough lines on its posterior half; the 

 third or posterior portion is sculptured with closely crowded, denticu- 

 late ridges which are separated by narrow, impressed lines. There are 

 seventeen (17) of these ridges in the space of one millimeter at the 

 posterior margin and about twenty-three cuticles to the space of one 

 millimeter on each ridge. The ridges of the posterior area of the central 

 part of the shell run parallel with the posterior margin of the central 

 part, joining the ridges of the posterior projection at a little more than a 

 right angle. Hinge irregularly sinuous. The posterior projection is 

 glazed by a moderately strong, translucent callus at the umbo. 

 31— Proc. Biol. Soc. Wash., XXI. 1908, (211) 



*An author's edition of this paper was printed and distributed December 7, 1908. 



