MOLLUSC A or THE ' CHALLENGER ' EXPEDITIOlSr. 515 



set, regular, sharp, and very minute lines, which very gradually 

 become more and more faint, but are still traceable even in 

 the full-grown shell. The colour is pare white, transparent, 

 and almost hyaline in the fresh shell, but in the dead shell 

 the interior (not, as usual, the exterior) layers of the shell 

 become opaque and chalky. The edge is very thin and irregu- 

 larly broken. At the apex the end is abruptly broken off in one 

 specimen, in the other there is an irregular fissure with an 

 internal lining process. In the specimen from St. 246, which 

 is full-grown but very short, a large, thin, irregularly shaped 

 process projects, which, being obliquely cut off somewhat 

 across the shell, supplies the anal orifice. L. 1'52, of young 

 specimens from St. 218 ; B. at mouth 0*12, at apex 0"026. L. 

 1'14, of old and broken specimen, St. 246 ; B. at mouth 

 0-23, at apex 0-14. 



Compared with D. leptosceles, "W., this is more curved, more 

 conical, and thus not nearly so attenuated. Compared with 

 D. agile, Sars, also, this is more curved, rather more conical, 

 and very much more delicate. It is likewise, when full-grown, 

 apparently larger than either. Than D. lubricatiom, Gr. B. Sow., 

 this broadens more rapidly, is more brilliant, the circular strise 

 are stronger, the longitudinal are finer, closer, and sharper. It is 

 also straighter than that species. Than D. pretiosum, Nuttall, 

 this broadens faster and is much more brilliant. 



In reference to the form of the apex, it may be observed that 

 the separation of the Dentalia by the absence (Dentalium) or pre- 

 sence {Enialis) of the cleft process cannot be maintained. In D. 

 ahyssorum, Sars, there are some with a fissured process, some with 

 a fissure without any process, some with neither fissure nor 

 process. There are cases in which the fissure is very regularly 

 formed, in others it looks as if it had been gnawed, in others it 

 resembles a break ; sometimes it is on the convex curve, as is the 

 general case, sometimes on the concave, as in D. inversum, Desh., 

 and in D. suhterfissum, Jeffr. ; sometimes it is irregularly lateral, 

 as occasionally in D. agile, Sars. 



10. Dentalium longiteobstjm, Beeve ; Beeve, Conch. Syst. ; 

 a I. pi. ii. 9. 



St. 189. Sept. 11, 1874. Lat. 9° 36' S., long. 137° 50' E. W. of 

 C. York, S.W. of Papua. 28 fms. Mud. 1 specimen. 



