246 LEPTOTHYRA. 



the literature relating to it, the group has never been made an? 

 object of critical systematic^ study. Previous monographers have 

 included the few species noticed at all in Turbo and Trochus. 



As to the family affinities of Leptothyra, the totality of its charac- 

 ters seem to me to indicate that its position is at the end of the 

 Turbinidce, rather than in the Trochidce, where it has been placed 

 by Von Martens, Try on and others. There is, in fact, no character 

 save the multispiral operculum, which at all affiliates Leptothyra to 

 the latter family; and, as I have shown, (p. 184), all the genera of 

 Turbinidce possess in the very young stage, multispiral opercula 

 precisely similar to that of Leptothyra ; so similar, indeed, that they 

 are scarcely distinguishable from it. It is altogether probable that 

 the Turbines are a divergent branch from the Trochid stem ; and 

 that Leptothyra and Collonia represent the primitive condition of 

 the entire family. 



The more complex structure of the operculum in the Turbinidce 

 and the reduction of the lateral teeth to five on either side, a 

 number frequently exceeded in the Trochidce, indicate higher rank 

 than the latter family. 



I am inclined to believe that the relationship of Leptothyra to 

 Collonia is very close, I am not, however, autoptically acquainted 

 with the latter genus ; and until we are in possession of fuller infor- 

 mation regarding it, J deem it best to retain them separate. 



I will briefly recapitulate the history of the 



Genus COLLONIA Gray, 1850. 



"Operculum circular, of many gradually increasing whorls, with 

 a convex external rib and central pit. Shell top-shaped, solid, 

 spirally striated, imperforated ; aperture circular, contracted ; inner 

 lip rather callous. Type, C. (Delphinula) marginata Lam." 

 (Gray.) 



This genus was described from a Paris Basin Eocene fossil, but 

 was evidently intended by its author to include also the recent spe- 

 cies of the type of Turbo sanauineus L. In this wider sense the 

 name was used by most authors until 1864, when P. P. Carpenter 

 proposed for the recent shells the name Leptonyx, which being pre- 

 occupied was changed to Leptothyra. Dall, Fischer, and a few 

 others, accepting this division, have restricted Collonia to the fossil 

 forms. My information regarding the genus as thus restricted is 

 derived from the original description copied above, and from the 

 figures of operculum and shell of the type species given by Deshayes 



