﻿DALL] REVIEW OE FROG-SHELLS AND TRITONS 1-5 



acter, and his work is still further complicated by a number of errors 

 in the matter of determining types. Nevertheless M. Cossmann 

 elucidates several groups which had been overlooked and by his 

 figures and descriptions lends aid to those who desire to study the 

 group more thoroughly. A full analysis of his arrangement will be 

 found in the ensuing nomenclatorial table. 



The Tritons are nearly allied to the Ranellas and to Dolium, rep- 

 resenting among the Tccnioglossa a group analogous to the Murices 

 among the Rhachiglossa, Their origin is traced to the Cretaceous 

 where are found some relatively small and delicately sculptured shells 

 having an external resemblance to Fusitriton, and possessing varices 

 which are irregularly distributed and more prominent internally than 

 externally, leaving on the surface of the internal casts axial sulci. 

 This genus named by Meek Trachytriton has been with much plausi- 

 bility suggested to be a precursor of the Tritons. This is of course 

 hypothetical since the dentition and the operculum can never be 

 known, yet it is to some extent supported by the presence in the 

 Claibornian Eocene of a somewhat intermediate type, the Rancllina 

 maclnrii of Conrad. In this form, while the varices are most promi- 

 nent internally, they are also well marked externally; the nucleus, 

 though small, is of the tritonoid type, while the spirally striated shell 

 has the general form of Trachytriton, rather fusoid than torticular. 1 



In the later Eocene the Tritons attained a well characterized de- 

 velopment, though the species are mostly of small or moderate size, 

 with the canal short, sometimes abruptly recurved, and the sculpture 

 more or less cancellate or nodulous, but usually more delicate than 

 that of the Neocene or living forms. An indication of the charac- 

 teristics of what, in later geological time, became well-marked genera, 

 is frequently perceptible ; as in the Personella of Conrad (P. septem- 

 dentata Gabb, of the Texan Eocene), which, though without the char- 

 acteristic lobe on the pillar and the wide spread callus on the body 

 whorl, has yet so much of the aspect of the Miocene and Recent 

 Persona (Montfort, = Distortrix Link) as to have been referred 

 to the latter genus by M. Cossmann. Persona, or Distortrix, was 

 fully evolved by the time the sedimentation of the lower Oligocene 

 took place in America, a characteristic species, D. crassidens of 

 Conrad, appearing in the Oligocene. 



In the Miocene Tertiary quite a full representation of the group 



1 1 do not know why M. Cossmann supposes that this species has never been 

 found since Conrad's time. It is not common but has been repeatedly collected 

 at Claiborne. A short variety of it seems to have been described by Whitfield 

 as Pisania claibornensis (Am. Journ. Couch., i, pi. xxvn, fig. 2, 1865). 



