PLEUROSTERNID./E. 45 



In addition to the families Pleurosternidae and Baenidae here treated, and tlu- 

 Plesiochelyidae provisionally included, the writer refers to this superfamily with- 

 out hesitation the Triassic genus Proganochelys, which has recently been so well 

 described by Dr. E. Fraas. Without doubt this genus forms the type of a distinct 

 family, the Proganochelyidae, characterized by the broad shell, the hinder border of 

 which is deeply scallopt, by the extremely broad vertebral scutes, by the series of 

 supramarginal scutes in front of the first costals and behind the last ones, and by 

 the mesoplastra, which meet at the midline and are enormously expanded at their 

 outer ends. The genus Proganochelys is the oldest turtle of which we have any 

 considerable knowledge, coming as it does from the Keuper, of the Trias. Cervical 

 vertebrae of a genus named Chelyzoon have been described bv Huene from the 

 Muschelkalk of Germany. They have been supposed to belong to the Cryptodira, 

 but there is little reason why thev should not be referred to the Amphichelydia. 



The most recent certainly known member of this subfamily comes to us from the 

 Uinta beds of Utah. Pleurosternon miocaenum Portis has been described from the 

 Tertiary near Lausanne, Switzerland, but it is based on a badly damaged plastron. 



I. Axillary and inguinal buttresses feebly develupt. Plastron usually not notcht behind; 



mesoplastra usually not narrowed at midline Pleurosternida 



i. Axillary and inguinal buttresses strongly developt; mesoplastra narrowing toward midline. . Baenidte 



Family PLEUROSTERNIDA Cope. 



\ family <>t Amphichelydia. Carapace with costals articulated to the peripherals bv close 

 sutures and bv gomphosis of ends of ribs. Plastron joined to the carapace by sutures and bv 

 narrow axillary and inguinal buttresses: the former ascending; to the first costal, the latter 

 attaining the borders of the fifth and sixth costals at their junction. In Helochelys the union of 

 carapace and plastron probably less intimate. Mesoplastrals meeting broadly at the midline, 

 not much expanded toward the outer ends. Exposed surfaces of carapace and plastron tuber- 

 culated or shagreened. Intergulars and intramarginals present. Skull elongated and pointed; 

 the bones mostly finely tuberculated. The cervical vertebrae are biconcave. Coracoids 

 disrallv expanded. 



So far as the writer knows, the name Pleurosternid;e for this family was proposed 

 by Prof. E. D. Cope in 1868 (Proc. Acad. Nat. Sci. Phila., p. 282) and was employed 

 by him at various times afterward. He regarded it as a family distinct from the 

 Baenidae. Both families appear to have been always included by him among the 

 Cryptodira. Lydekker (Cat. Foss. Reptiha, in, p. 205) includes in it the Baenidae. 

 Baur (Proc. Acad. Nat. Sci. Phila. 1 St; 1 , p. 428) thinks it better to leave Ba'ena in a 

 distinct family, nearly related to Pleurosternon. lo the present writer each group 

 appears to be worthy of family rank. 1 he genus Helochelys, of the Cenomanian of 

 Germany, evidently belongs with the Pleurosternida'. Pleurosternon is found in the 

 Purbeck and Portland Oolite of England. A species described bv Roemer as 

 Emys menket, from the Wealden of Germany, is believed to belong to Pleuro- 

 sternon. Portis has described P. mtoccenum from the Tertiary near Lausanne, 

 Switzerland. In our own country, it appears that Glyptops existed from the 

 Upper Jurassic through the Lower Cretaceous (G. coelatus) and the Benton (G. 

 pervicax) into the Denver (G. depressus) of the uppermost Cretaceous. 



Genus GLYPTOPS Marsh. 



Carapace deprest. Exposed surfaces of the shell rough with small tubercles and twisted 

 ridges. Xeurals hexagonal, with the broad end in front. Costo-marginal sulci mostly below 

 the costo-peripheral sutures. Axillary buttresses reaching border of first costals. Inguinal 

 buttresses each entering an excavation at lower borders of fifth and sixth costals. Mesoplas- 



