146 CADULUS-POLYSCHIDES. 



middle of the posterior (i. e. convex curve) wall ; a little farther in, 

 a thin, narrow, circular callus runs round the opening. 



Length O35 in. breadth at mouth O032 ; broadest 0'055 ; apex 

 0*022. (Watson). 



Levuka, Fiji, 12 fms. (Challenger). 



Siphodentalium dichelum WATS., Journ. Linn. Soc. Lond., xiv, p. 

 521 (1879) ; Chall. Rep., p. 15, pi. 2, f. 7. 



This is much larger than S. tetraschistum Wats., and much less 

 cylindrical, being much more contracted towards the mouth. The 

 posterior internal rib is a curious feature. It shows through the 

 shell like a crack or depression, but is a true internal rib ( Watson). 



C. PRIONOTUS (Watson). PL 26, fig. 74. 



Shell long, narrow, tapering, gently contracted at the mouth, 

 slightly bent throughout ; rather strong, polished, but hardly bril- 

 liant, translucent white. Sculpture : very faintly transversely stri- 

 ated on the surface, and a very minute flocculence in the same direc- 

 tion in the texture. For the breadth of the shell the mouth is large, 

 perfectly round, oblique, with a smoothly rounded edge, which is 

 sharp on its inner margin. The apex is small, much chipped, but 

 that in such a way as in all the specimens to produce a shallow 

 rounded hollow on either side, with a sharp, projecting point before 

 and behind. Within the opening a short excessively minute riblet 

 runs out along the middle of the posterior wall ; it shines through 

 the shell like a depression, being a little more transparent than the 

 shell-wall. 



Length 0'328 in. breadth at mouth 0'028 ; greatest 0'039 ; at apex 

 0-013 inch. (Watson). 



Raine Island, Cape York, N. E. Australia, 155 fms. (Challenger). 



Siphodentalium prionotum WATS., Journ. Linn. Soc.-Lond., xiv, 

 p. 522 (1879) ; Chall. Rep., p. 16, pi. 2, f. 9. 



This species differs from the previous [dichelus] in being much 

 narrower and having no swelling. From Siphodentalium tetraschis- 

 tum Wats, it differs in being more elongated, more attenuated be- 

 hind, and in the character of the posterior opening. ( Watson). 



Section POLYSCHIDES Pilsbry & Sharp, 1897. 



Shell inflated above the middle or not much bulging ; apex cut 

 into a number of lobes, generally four, by as many slits. Type C. 

 (Polyschides) tetraschistus Wats. 



