92 TOLtTTID^. 



Form, and Loc. — Eocene : Broken river, Trelissick (ITo. 5), South 

 Island, New Zealand. 



G. 9513. Two casts. Sir James Hector Coll. 



G. 9515. An example of the senile stage ; outer margin ex- 

 tremely thick ; the callosity communicating anteriorly with the 

 widespread deposit on the columellar surface. 



Sir James Hector Coll. 



Family YOLUTID-Sl. 



The fine collection of larval shells appertaining to this family 

 in the Museum collection of Australasian Tertiary moUusca, 

 suggests a few words concerning the origin and evolution of the 

 groups they represent, as deduced from the study of the proto- 

 conch, and early stages of growth of the shell generally. 



The striking characters presented by the protoconch in living 

 forms of the family have long attracted attention, and were to 

 a limited extent taken advantage of in describing genera and 

 species. Amongst others who place a high value on the larval 

 shells for systematic purposes is M. Crosse, of Paris, who reviewed' 

 the living species referred to the family, and was willing to 

 concede, in at least one instance,^ that the phenomena of the 

 protoconch might be of generic importance. Eut it was reserved 

 for Professor W. H. Dall,' of "Washington, who studied fossil as 

 Avell as living representatives of the Voltjtid^ to throw the 

 greatest light on this matter. He stated his conviction that the 

 family descended from the Mesozoic " Fusing. " In the Mesozoic 

 transition forms the larval covering was shelly and minute, its 

 upper surface like a minute Co7iulus or Hyalinia. This indicates, 

 he believes, that those forms found their benefit in the production 

 of a large number of small shell-bearing larvae, rather than in 

 a small number of large ones. This holds good for all the 

 Mesozoic forms, at least in America, and for all the exotic 



1 Journ. de Conehyl. Z" ser. t. xi. 1871, p. 263 et sqq. 



2 Op. cit. p. 275. 



3 Bull. Museum Comp. Zool. Harvard, vol. xviii. 1889, p. 452; Proc. U.S. 

 Kational Museum, vol. sii. 1890, p. 311; and especially Trans. "Wagner Free 

 Inst. Sci. PMlad. vol. iii. 1890, p. 57 et sqq. 



