118 THE WASATCn AND BKIDGER FAUN.E. 



Tliero were evidently several species of Trionyx during both the 

 Wasatch and Bridger epochs ; but the specimens found are generally so 

 fragmentary, that it is difficult to ascertain what characters can be relied on 

 to distinguish them. In the Paleontology of New Mexico (Wheeler's 

 Report) I enumerated five as occurring in the Wasatch formation of that 

 region, but I am not sure that more than three of tliem will ultimately be 

 found to deserve that distinction. In vay collection from the Bridger beds 

 I have three manifestly distinct species, and I am compelled to admit two 

 others. Of the five, I regard two as identical with New Mexican Wasatch 

 species, and one as common to the Bridger and Wasatch beds of Wyoming. 

 The proper definition of the doubtful species must be left to future discovery 

 of better material. 



The Eocene Trionyches may be distinguished in tabular form as follows : 



I. Sculpture of the extremities of the costal bones thrown into ridpes. 



a Superficial layer of costal boues overhanging rib extremities. 



Eidges clo.se together T. lepiomitus. 



Eidges widely separated T. cariosits, 



a a Superficial layer of costal bones, sloping into free rib ends. 



Eidges widely separated T. raduln.i. 



Ridges do.se together, interrupted and vermiform .... T. ventricosux. 



II. Sulpture of the extremities of the costal boues honeycombed or 



punctate. 



Carapace with .seuljjture all honey-combed ; six vertebral bones ... T. vintaensis. 



Carapace covered with pits which are little wider than their inter- 

 spaces ; seven vertebral bones T guttatm. 



Carapace with longitudinal ribs crossing the ends of the costals; 



pits small T. concent ricus. 



Carapace with longitudinal ribs along its middle ; seven vertebral 



bones ; pits not large T. heteroglyptua. 



III. Sculpture of extremities of costal bones, consisting of small 



tubercles formed of the broken ridges. 

 Carapa<'<' honeycombed with large fossaj ; no ribs ; seven verte- 

 bral bones T. sciitumantiquum. 



Tlie Wasatch species are : T. hptomitus, T. cariosits, T. radidus, T. 

 ventricosus, T. guttatus, and T. scutxiinantiquum. The Bridger species are : 

 T. radulus, T. uintaensis, T. guttatus, T. conccntricus, T. heteroglyptus, and 

 T. scutuniantiquum. 



