SIPHONODENTALIUM. 135 



I have placed this species temporarily in Dentalium, as the tips 

 of the four specimens examined are all damaged. Possibly more 

 perfect examples may exhibit slits as in Siphodentalium (Smith). 



The single specimen we have seen (in Coll. U. S. Nat. Mus.) is so 

 similar to E. quinquangularis that we adopt Mr. Smith's suggestion 

 that it may belong near that species. The apical slitting is a vari- 

 able character, and rarely developed in Entalina. 



Genus SIPHONODENTALIUM M. Sars, 1859. 



Siphonodentalium M. SAKS, Forh. Videnskabs-Selskabet i Chris- 

 tiania, Aar 1858, p. 52 (1859). Om Siphonodentalium vitreum, etc., 

 Univ. Programme for 1861. G. O. SARS, Moll. Reg. Arct. Norv., p. 

 103, restricted to S. vitreum. 



Siphodentalium MONTEROSATO, Journ. de ConchyL, 1874, p. 258 r 

 and in subsequent papers. JEFFREYS, Ann. Mag. Nat. Hist. (4), 

 xix, p. 155 (1877), and in later papers. WATSON,Challeriger Report 

 on Scaphopoda (1886). 



Siphonodontum or Tubidentalium LOCARD, Prodr. Mai. Fr. in 

 Ann. Soc. d'Agricult. Lyon, 1886, p. 149, footnote ; emendations of 

 Siphonodentalium. 



Shell an arcuate, slightly tapering tube, largest at the aperture, 

 circular or nearly so in section, and smooth externally. Apex 

 rather large, typically slit into lobes, but sometimes simple. Foot 

 capable of expanding into a terminal disk. Type S. lobatum. 



A widely distributed genus of few species, confined to deep water 

 except in high latitudes. 



G. O. Sars divides Siphonodentalium into two groups : Siphono*- 

 dentalium (restricted), in which the apex of the shell is cut into 

 lobes (pi. 23, fig. 12), and the terminal pedal disk is concave in 

 the middle, without a central process (pi. 23, figs. 9, 18). 



Siphonentalis Sars, having the apex of the shell entire (pi. 24, fig. 

 42), and the terminal disk of the foot convex in the middle, with a 

 long central process (pi. 24, fig. 40). 



This division is based upon too few species to warrant the adop- 

 tion of two genera ; the more as we have found the development of 

 slits to be a feature of minor importance in other groups of Scaplio- 

 poda. 



Key to Species of Siphonodentalium. 



I. Apex with slits. 



a. Slowly tapering ; apex 6-lobed ; length 10 mill., lobatum. 



