XII REMARKABLE ABYSSAL MOLLUSCA 377 



Sea, have given us the remarkable new forms Benthohia (possibly 

 akin to Admete), Mcsorhytis (a sub-genus of Fasciolaria hitherto 

 only known from the Cretaceous of North America), and Bentho- 

 dolium (possibly = Oocorys), a genus akin to Cassis. 



In his report on the Pelecypoda obtained by the Challenger, 

 Mr. E. A. Smith remarks that as a rule " very deep-water 

 ' benthal ' species certainly have a tendency to be without 

 colour and of thin structure, facts no doubt resulting from the 

 absence of light, the difficulty of secreting lime, the scarcity of 

 food, and other unfavourable conditions of existence." At the 

 same time, he notices that most of the species obtained belong to 

 genera which, even when occurring in shallow water, are thin and 

 colourless, e.g. Neaera, Lima, Cryptodon, Ahra, Vcrticordia, etc. 

 Deep-water species of such genera as have a decided periostracum 

 {Malletia, Limopsis, Lcda, Nucula, Area) retain it with little if 

 any modification. The deep-water Pelecypoda of the Atlantic 

 and Pacific Oceans present no special features of interest. The 

 species are few in number, and the genera are not remarkable 

 either for novelty or peculiarity of form. 



The greatest depth at wnich Pelecypoda have been obtained 

 is 2900 fath. mid North Pacific (Callocardia pacifica Sm., Alra 

 profmidorum Sm.) ; the greatest depth at which Gasteropoda have 

 been obtained is 2650 fath. South Atlantic {Stylifer hrychius 

 Wats.), both by the Challenger. The deepest Challenger Nudi- 

 branch came from 2425 fath., and the deepest Chiton from 2300 

 fath. The greatest depth ever dredged is 4575 fath. off the east 

 coast of Japan. 



