EAST AMERICAN SCAPHOPOD MOLLUSKS. 89 



KEY TO THE SPECIES OP THE SUBGENUS SIPHONODENTALIUM. 



Shell smooth. 



Apex 6 lobed lobatum, page 89 . 



Apex 2 lobed. 



Less slender shell (5.5 mm. by 1.23 mm.) tytthum, page 91. 



More slender shell (7 mm. by 0.8 mm.) verrilli, page 91. 



Shell not smooth striatinmn, page 90. 



SIPHONODENTALIUM (SIPHONODENTALIUM) LOBATUM Sowerby. 



Plate 16, figs. 1, 9. 



1851. Dentalium vitreum Sars, Ny. Mag. f. Naturviden., vol. 8, p. 178 (not of 



Gmelin, 1788). 

 1860. Dentalium lobatum Sowerby, Thes. Conch., vol. 3, p. 100, pi. 3, fig. 44. 

 1860. Dentalium lobatum Sowerby, Reeve, Conch. Icon., vol. 18, pi. 5, fig. 36. 

 1880. Siphonodentalium vitreum, Verrill, Proc. U. S. Nat. Mus., vol. 3, p. 394. 

 1882. Siphonodentalium vitreum, Verrill, Trans. Conn. Acad. Arts and Sci., vol. 



5, pt. 2, p. 557. 



1896. Dentalium lobatum, Clessin, Conchylien Cab., vol. 6, pt. 5, p. 15, pi. 4, 



fig. 6. 



1897. Siphonodentalium lobatum, Pilsbry and Sharp, Tryon's Man. Conch., vol. 



17, p. 136, pi. 23, figs. 8 to 21. 

 1901. Siphonodentalium lobatum, Whiteaves, Cat. Mar. Invert. Canada, p. 153. 

 1915. Siphonodentalium Zobaium, Johnson, Occ. Papers Boston Soc. Nat. Hist., 



vol. 7, No. 13, p. 83. 



An extensive European bibliography is omitted. 



The shell is short, thin but solid, and so rapidl}- increasing in diam- 

 eter as to give to it a "stumpy" appearance. It is regularly, deeply 

 curved, with a rather large apex. The anterior aperture is oblique 

 and shell section round. The color is of a milky white, the shell 

 being of vitreous texture, translucent, and sometimes quite trans- 

 parent. The surface is smooth and sometimes highly polished. It 

 is without sculpture. The apical characters consist of six lobes, a 

 subtriangular one on each side, with two on the convex, and two 

 short ones on the concave side. These apical features, however, are 

 rarely well preserved on account of the fragile nature of the lobes. 



Measurements are: 



Length, 16 mm.; diameter, 2.7 mm.; arc, 1.8 (Fmmark). 



Length, 17 mm. ; diameter, 2.5 mm. ; arc, 2. Gulf of St. Lawrence. 



LenSth, 19 mm. ; diameter, 3 mm. ; arc, 2. Lofoten. 



This^'is a deep cold water species of the northern Atlantic and Arctic 



Oceans. • i i i. • ♦u t ^^ 



A critical comparison of American specimens with lots m the Jel- 

 freys collection leaves no room for doubt as to their specific identity 

 Three lots from off Marthas Vineyard in 100 to 384 fathoms, and 

 from off Cape Hatteras in 516 fathoms, are smaller than the dunen- 

 sion above given. As they are but fragments I have not separated 



