EAST AMERICAN SCAPHOPOD MOLLUSKS. 83 



DENTALIUM (BATHOXIPHUS) DIDYMUM Watson. 



Plate 14, fig. 10. 



1879. Dentalium didymum Watson, Journ. Linn. Soc. London, voL 14, p. 517. 

 1885. Dentalium, didymum Watson, ChaUenqer Report (Scaphopoda), p. 10, pi. 1, 



fig. 11. 

 1897. Dentalium enciculus didymum, Pilsbry and Sharp, Tryon's Man. Conrh., 



vol. 17, p. 123, pi. 7, fig. 20. 



The shell is extremely attenuated, slightly curved, and a little 

 flattened laterally, especially toward the convex curve, giving a 

 trigonal section rather than that of a flattened oval. It is porcella- 

 nous in texture, of a brilliant surface, and pure white in color. It is 

 sculp tureless but for "faint indications of longitudinal texture," and 

 some very fine encircling growth lines. Xo apical features are noted 

 in Watson's description. 



The type measures — length, 1.08 inches; diameter, 0.6 inch (27 AS 

 mm. by 1.52 mm.). The type was taken at Challenger Station 24, 

 north of Culebra Island, in 390 fathoms, and is in the British Museum. 



I have seen no authentic specimens. The diagnosis indicates a 

 shell belonging to the grouj) of Dentalium ensiculus, but hardly to 

 be united to it even as a subspecies. A poor specimen in the National 

 Museum collections from Cape Catoche, Yucatan, Cat. Xo. 314575, 

 U.S.N.M., 25 fathoms, is possibly referable to this species; also three 

 fragmentary specimens from Barbados, Cat. Xo. 314905, U.S.X.M., 

 taken by the State University of Iowa Expedition at their station 6, 

 in 100 fathoms; also one young specimen, Cat. Xo. 314906, U.S.X.M ., 

 from the State University of Iowa Expedition Station 2, Carlisle 

 Harbor, Barbadoes, in 12 fathoms. 



In these shells the apical features are indicated as a broad square 

 notch on the convex side. 



Subgenus COMPRESSIDENS Pilsbry and Sharp, 1897. 

 1897. Compressidens Pilsbry and Sharp, Tryon's Man. Conch., vol. 17, p. 123. 



The shell is small, decidedly ta])ering, conspicuously compressed 

 between the convex and concave sides; weakly sculptured, nearly 

 smooth, with its apical orifice simple without either slit or notch. 



KEY TO THE SPECIES OF THE SUBGENUS COMPRESSIDENS. 



Shell strongly compressed; no constriction of caliber; moderately curved. 



pres.ntm, page 83. 

 Shell not strongly compressed; constriction of caliber; considerably curved. 



ophiodon, page 84. 



DENTALIUM (COMPRESSIDENS) PRESSUM Pilsbry and Sharp. 



Plate 14, figs. 3, 6, 8. 

 1879. Dentalium compressum Watson, Journ. Linn. Soc. London, vol. 14, p. 516 



(notOrbigny, 1850). 

 1881. Dentalium compressum, Dall, Bull. Mus. Comp. Zool., vol. 9, p. 38. 

 1885. Dentalium compressum Watson, Challenger Report (Scaphopoda), p. 9, ])1. 



1. fig. 9. 



