232 



FOSSIL TURTLES OF NORTH AMERICA. 



having the direction of the ridges of sculpture running at right angles with the sulcus. The 

 inner surface of the bone is removed, so that the thickness of the fragment can not be deter- 

 mined. It was more than 6 mm. 



The piece of medium size has a sutural edge along one side. The thickness is 6 mm. 

 where thickest, 5 mm. where thinnest; and it may be the fragment whose measurement Cope 

 gave. The smallest piece of bone is only 3 mm. thick. 



This species is distinguish! especially by its sculpture. It is thus described by Cope: 



It consists, in the Compsemys imbricarius, of excavations bounded on the sides by a short ridge 

 each, which [excavations] alternate with each other. Thus each bounding ridge terminates abruptly 

 at the fundus of one of the fossae, while the other end of the fossa rises and contracts into another 

 ridge. The result is precisely that seen in the interior sculpture of Saracenic domes and niches, 

 and is one quite unique among tortoises. The direction of the ridges is at right angles to the costal 

 dermal sutures. 



Cope states that three of the fossx measure in length 6.5 mm. and crosswise, 5 mm. In the 

 case of the largest of the three fragments of the type three fossae taken together measure 7 mm. 

 and crosswise, 6 mm. 



While this style of ornamentation appears to be very peculiar, something scarcely dis- 

 tinguishable in pattern may be seen here and there on the carapace of B. variolosa, and for 

 that reason the present species has been referred to Basilemys. In fact Cope has labeled as 

 Compsemys imbricaria some fragments the sculpture of which appears quite identical with that 

 of B. variolosa. With these latter fragments, however, there is what seems to be the thickened 

 rim of the front of the carapace (fig. 290, No. 6100 A. M. N. H.), and this is plainly different 

 from that of B. variolosa. Evidently there is another species occurring with B. variolosa, 

 related to it, but differing in important characters. For this species we may for the present 

 retain the name Basilemys imbricaria. 



The remains of this form were collected in 1876, in the Judith River beds of Montana, by 

 Mr. Charles H. Sternberg. 



Fig. 290 represents a section across the supposed anterior peripheral, No. 6100 A. M. N. H. 



The part of this peripheral which joins the costal 

 is missing. On the under side it appears to extend 

 backward to the line reacht by the soft skin, a 

 distance of 27 mm. from the free border. The 



2 _ o extreme thickness of the fragment is 16 mm. The 



upper surface is slightly convex; the lower surface 

 FIGS. 290 AND 291. -Basdemys imbricaria. strong i y so . The ornamentation is coarse, there 



Sections. X. No. 6101 A. M. N. H. being 3 fossae in 9 mm. This peripheral differs from 

 190. Section across peripheral. one j n tne sam e region of B. variolosa in having 



291. Section across border of xiphiplastron. , , f , -jri_L 



the sculptured surface on the under side of the bone 

 much narrower from the free edge to the skin line in proportion to the thickness of the bone. 



It is to be noted that these coarsely sculptured fragments possibly do not belong to B. 

 imbricaria. 



In the Cope collection there is another fragment (No. 6101) which possesses a sculpture 

 like that of the specimens just described, and this is evidently a portion of the left xiphiplastron 

 (fig. 291). There are 3 fossae in 8 mm. It differs from that of B. variolosa in having a sharp 

 border separating the lower surface from the surface which looks outward and upward. In 

 B. variolosa the lower surface of the hinder lobe rounds gradually into the upper surface. 



Professor Cope has labeled as Compsemys imbricaria other specimens from the Judith 

 River beds which have a sculpture similar in pattern but much more delicate. In these 

 (No. 6103 A. M. N. H.), some of them fragments of costals, there are 4 fossae in a line 5 mm. 

 long. The scutal sulci are thread-like. Other fragments, peripherals from the bridge perhaps, 

 have similar ornamentation but the sulci are very broad. It seems very probable that the 

 fragments here described belong to more than one species, but the discovery of additional and 

 much better materials will be required in order to determine the structure and generic position 

 of Cope's Compsemys imbricaria. 



