82 



BULLETIN 111, UNITED STATES NATIONAL MUSEUM. 



1889. Dentalium ensiculwi, Dall, Bull. Mus. Comp. Zool., vol. 18, p. 428, pi. 27, 



fig. 12. 

 1889. Dentalium ensiciilus, Dall, Proc. U. S. Nat. Mus., vol. 12, p. 294. 

 1897. Dentalium ensiculus, Pilsbry and Sharp, Tryon's Man. Conch., vol. 17, 



p. 121, pi. 7, figs. 7-10. 

 1903. Dentalium ensiculus, Dall, Bull. 37, U. S. Nat. Mus., p. 76. 



The shell is fairly strongly arched, with chief curvature in its pos- 

 terior third. It is slowly, regularly increasing in diameter, decidedly 

 flattened laterally, and has a more or less sharp keel developed on 

 both the convex and concave sides, becoming, however, less sharply 

 angular near the anterior aperture in adult specimens. Occasion- 

 ally a bluntly angulated keel appears on the flattened sides. The 

 aperture is a flattened oval. The color is grayish white, the slightly 

 roughened surface is of an oily appearance rather than polished; 

 the shell is either translucent or quite opaque. No sculpture is 

 present, but some concentric lines of growth are more or less promi- 

 nent. There is a very wide sc^uare apical notch on the convex side, 

 which is over half the diameter of the tip. 



Measurements are: 



Length, 30 mm.; greater diameter, 3 mm.; lesser diameter, 2 mm.; 

 arc, 2.2 (Georges Bank). 



I^ength, 31 mm.; greater diameter, 2 mm.; lesser diameter, 1.25 

 mm.; arc, 2.25 (St. Vincent). 



Length, 19 mm.; greater diameter, 1.5 mm.; lesser diameter, 1 

 mm.; arc, l.S (Yucatan). 



Variations are to be noted in size and in the degree of sharpness 

 of keels. AntiUean specimens are somewhat more slender. Northern 

 specimens are usually more chalky and less compact in texture. I 

 can not separate these American shells from the east Atlantic speci- 

 mens in the Jeffreys collection. 



It is a deep-water species of probably very considerable geographic 

 range on the ocean floor. West Atlantic records in the National 

 Museum collection are as follows: 



Locality. 



fieorees Banks, U. S. B. F. Station 2570 



Off Nantucket, U. S. B. F. Station 2714 



Off Nantucket, V. S. B. F. Station 2715 



Off Nantucket, U. S. B. F. Station 2713 



Off Delaware, U. S. B. F. Station 2716 



Off Fernandina, Florida, U. S. B. F. Station 2668 

 Off Cape Florida, Florida, U. S. B. F. Station 



2644. 

 Off Cape San Bias, Florida, U. S. B. F. Station 



2399. 



Off Habana, Cuba (?) 



Yucatan Strait Blake Station 



St. Vincent, West Indies, Blake Station 240 



Off St. Barts, U. S. B . F. Station 2750 



Remarks. 



1,813 fins., 37°, glob. oz. 

 1,825 fms., br. oz. 

 1,753 fms., br. oz. 

 1,859 fms., br. oz. 

 1,631 fms., br. oz. form. 

 294 fms., 46.3° gy. s. del. eo. 

 193 fms., s., 43.4° gy.s. 



196 fms., gy. m. 51.6. 



1,024 fms. (Rush). 



640 fms. 



464 fms. 



495 fms., 44.4°. 



