136 SIPHONODENTALIUM. 



a'. Rapidly tapering ; apex with at least two slits ; length 5*5 



mill., tytthum. 



a". Apex 2-slit, the clefts dorsal and ventral ; length 8-9 mill., 



teres. 

 II. Apex simple, unslit. 



a. Atlantic and Mediterranean species. 



b. White, but slightly pellucid ; aperture 3 times as 



wide as apex ; length 6 mill or less, lofotense. 

 b'. Very pellucid, smooth ; aperture twice the width of 



apex ; length 4*5 mill., affine. 



b". Transparent, obliquely banded with opaque white ; 



sharply scratched with minute transverse strise; 



length 3 mill., pusillum. 



a! From Torres Strait. Very gradually tapering, translucent 



and transparent in alternate bands; excessively minute 



longitudinal strise ; length about 3'5 mill., eboracense. 



Section SIPHONODENTALIUM (restricted). 

 S. LOBATUM (Sowerby). PI. 23, figs. 8 to 21. 



Shell cylindric, very smooth and glossy, thin, pellucid, glassy ; 

 arcuate ; slowly tapering from the aperture to a rather large apex, 

 which is cut into six lobes or teeth : a subtriangular one on each 

 side, two contiguous lobes on the convex side (figs. 14, 19), and two 

 very short lobes on the concave side (fig. 13). Aperture circular, 

 oblique. Length 10 mill. 



Arctic Ocean from Spitzbergen and Novaia Zemblia to Finmark 

 (Sars and others) ; North Atlantic between Faroes and Orkney Is., 

 560 fms. ; of coast of Portugal, 740-1095 fms. (Lightning and Por- 

 cupine Expeditions) ; Gulf of St. Lawrence, 150-200 fms. (White- 

 aves) ; Gulf of Maine and off Martha's Vineyard (U. S. Fish Com- 

 mission). 



Dentalium vitreum M. SARS, Nyt Mag. f. Naturvidenskaberne, vi, 

 p. 178 (1851). Not Dentalium vitreum Gmel. Syst. Nat. (13), p. 

 4739. 



Siphonodentalium vitreum M. SARS, Forh. Videnskabs-Selskabet i 

 Christ., Aar 1858, p. 52 (1859) ; Om Siph. vit.,en ny Stagt og Art 

 af Dentalidernes Familie, Universitets-Program for fo'rste Halvaar, 

 1861, pp. 29, pi. 1-3 (except figs. 78-81) ; Om de i Norge Forekom- 

 mende Fossile Dyrelevninger fra Qvarteerperioden, Univ. Progr., 

 for 1864, p. 42, pi. 3, f. 99 (1865). G. O. SARS, Moll. Reg. Arct. 



