EMYDID.&:. 



345 



Hybemys arenaria Leidy. 



Hybemys arenanus, LEIDY, Proc. Acad. Nat. Sci. Phila. 1871, p. 103; Fifth Ann. Report U. S. Geol. 

 Surv. Montana, etc., 1871, (1872), p. 369; Contrib. Ext. Vert. Fauna West. Terrs., 1873, p. 174, 

 plate xv, fig. 9. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 448. 



This species was based by Dr. Leidy on a single peripheral and a fragment of a costal of 

 an emydoid turtle believed to be about the size of Chrysemys picta or Clemmys guttata. These 

 bones were secured on Little Sandy Creek, Wyoming. The level is that known as horizon A 

 of the Bridger Eocene. The specimen belongs to the Academy of Natural Sciences, Phila- 

 delphia. 



The bones are described as being unusually thick in proportion to the width. The sulci 

 are strongly markt. The rib-heads are stout. The outer portion of the upper surface of the 

 peripheral is strongly defined by the groove of the costo-marginal sulcus. At the anterior and 

 the posterior ends of the peripheral there is seen a semicircular boss. It is inferred that the 

 other peripherals had at each end a similar semicircular boss, so that around the carapace, 

 on the peripherals, there was a row of hemispherical elevations, each of which was crost by the 

 suture between the two peripherals on which it rested. 



Genus CHRYSEMYS Gray. 



Shell smooth, deprest, without traces of dorsal keel. Carapace not serrated behind; 

 often dentated in front. Plastron with broad anterior and posterior lobes. The anterior lobe 

 with a distinct lip which is often dentated. Posterior lobe truncated behind, scarcely notcht. 

 Inguinal buttresses articulating with the fifth costals. Alveolar surfaces of the upper jaw 

 narrow in front, increasing in width backward, never very broad, and with a feeble longi- 

 tudinal ridge. Choanae on line joining the fronts of orbits. Alveolar surface of lower jaw with 

 a longitudinal groove bounded inwardly by a sharp ridge. Symphysis of lower jaw very short. 



The type of this genus is Chrysemys picta, the painted turtle of the Atlantic states of the 

 Union. From the Alleghenies to the Mississippi River the genus is represented by C. cinerea. 

 West of the Mississippi river we find C. belli; while in the lower region of that great stream is 

 found another species or race, C. dorsalis. 



To the writer it appears that these species form a natural group worthy of generic rank, 

 and that C. timida is an extinct member of that group. 



Chrysemys timida sp. nov. 

 Plate 46, fig. 2; test-fig. 449. 



Chrysemys timida is founded on a shell which belongs to the E. & M. Museum of Princeton 

 University, and has the catalog number 10853. ^ was collected by the University expedition, 

 in the Equus beds of Sheridan County, Nebraska, not far from the Niobrara River. Doubtless, 

 as it lay in the matrix it was complete; but from the vicissitudes of collecting, transporting 

 and preparing, it has suffered somewhat. The matrix is sand that scarcely coheres and the 

 bone itself is friable. In its present condition most of the peripherals of the left side are gone 

 and considerable portions of those of the right side. The other parts of the carapace are in 



good condition and display well the bone 



Dimensions of vertebrals. sutures and the sulci. Portions of the 



plastron have crumbled away, but the 

 structure can be pretty satisfactorily 

 determined. 



The individuals of this species reacht 

 a considerable size, compared with those 

 now living, being about equal to C. belli. 

 The extreme length of the carapace 

 (plate 46, fig. 2; text-fig. 449) was perhaps 

 a little more than 160 mm.; the breadth, 

 about 120 mm. The shell was evidently 



