EAST AMERICAN SCAPHOPOD MOLLUSKS. 59 



KEY TO THE SPECIES OF THE SUBGENUS FISSIDENTALIUM . 



Tip hexagonal; size medium (74 mm. by 10 mm.). 



Maximum of 24 riblets, color yellowash florideme pa^e 64 



Tip 16 ribbed. ' " , » ■ 



Maximum of 90 riblets; ashen or mouse color. 

 Riblets persisting to aperture. 



Very large (length 108 mm. by diameter 14 mm. ) mrridtonale, page 59. 



Stouter forms (diameter 14 mm.) m. meridionale, page 61. 



Slenderer forms (diameter 10 mm.) /». jmnolcense, page 62. 



Riblets not persisting to aperture. 



Medium sized (length 96 mm. by diameter 10 mm. ) m. rerrilli, page 62. 



Maximum of 50 riblets; yellowish brown. 



Smaller size (length 50 mm. by diameter 7.5 mm. ) amphialum, page 59. 



DENTALroM (FISSIDENTALIUM) AMPHIALUM Watson. 



Plate 8, fig. 1. 



1879. Dentalium amphialum Watson, Journ. Linn. Soc. London, vol. 14, p. 510. 

 1885. Dentalium amphialum Watson, Challenger Report, Scaphopoda, etc. p. 8 



pi. 1, fig. 3. 

 1897. Dentalium (Fissidentalium) amphialum, Pilsbry and Sharp, Man. Concli.. 



vol. 17, p. 71, pi. 8, fig. 37. 



Shell is long, large, almost straight, and equally curved. The color 

 is a dirty brownish yellow; the texture is chalky, a soft outer layer 

 covering a porccllanous portion, with many shell layers shown in sec- 

 tion. There are 50 slightly raised primary riblets with shallow open 

 spaces between, the riblets disappearing anteriorly. No transverse 

 sculpture is present beyond growth line "scratches," becoming 

 "harsh" and "broken" toward the anterior end of the cylinder. 

 There is a short irregular apical fissure on the convex side. 



The type is in the British Museum. It measures — -length, 50 mm. ; 

 diameter, 7.5 mm. 



Taken off the mouth of the La Plata River in 1,900 fathoms, blue 

 mud, temperature 33.1*^ F., Challenger Station No. 323. 



This species is not represented in the National Museum collection 

 and I have seen no examples. Doctor Watson's description indicates 

 a species very close to Dentalium meridionale. 



DENTALIUM (FISSIDENTALIUM) MERIDIONALE Pilsbry and Sharp. 



In 1884 Professor Verrill published his description of Dentalium 

 solidum, a species from deep water off Block Island and the Delaware 

 Capes. A very full series of this large Dentalium, including many 

 living examples, had been taken the year before by the Albatross from 

 numerous stations off southern New England. Five years later, in 

 reviewing the Scaphopods of the coast, Doctor Dall united this species 

 with the European D. candidum, described by Jeffreys in 1877, from 

 northeast Atlantic stations in 410 to 1,750 fathoms. In 1897 Pilsbry 

 and Sharp, in their monograph of the order, accepted Dr. Dall's dis- 

 157582°— 20 5 



