494 



FOSSIL TURTLES OK NORTH AMKRICA. 



Most of the costals are widened at their distal ends. The costals of the sixth pair join 

 medially without interruption. Those of the eighth pair are directed backward, and join for 



their full length in the midline, their distal ends forming 

 the median portion of the border of the shell. The tree 

 borders of the median costals are beveled off at an angle of 

 about 45 ; the more posterior ones are rounded on the edge. 

 The thickness in the middle of their length is usually 

 close to 6 mm. at the sutures, while thru the rib the thick- 

 ness amounts to 8 mm. At their distal ends the thickness 

 at the sutural edges is 10 mm. and thru the rib about 12 

 mm. The ribs are quite prominent on the under side of 

 the costal bones, and occupy about two-thirds of the width 

 of the plate. Most of the bodies of the dorsal vertebra; 

 are eroded awav, and there is exposed a cast of a portion of the neural cord about 5 mm. in 

 diameter and 160 mm. long. 



The sculpture (plate 96, fig. 2) appears to agree well with that of the type of this species; 

 but it has suffered somewhat from weathering. On the middle of the costals there are 4 or 5 

 pits in 10 mm. On the neurals and the distal ends of the costals they are somewhat smaller; 

 on the nuchal and in places on the hindermost pair of costals, somewhat larger. 



This specimen reveals to us the convexity of the carapace, as well as the form of the hinder 

 border. 



Two carapaces have been submitted to me for examination, which had been collected by 

 Prof. J. B. Hatcher in the |udith River beds on Fish Creek, Montana. These bear the 

 numbers 445 and 541 of the Carnegie Museum, Pittsburg. No characters are observed which 

 serve to distinguish these carapaces from that of the type of A. beechen. It is not improbable, 

 however, that they belong to a distinct species. 



Prof. O. C. Marsh, as cited in the synonymy, has reported Trionyx foveatus from the 

 Ceratops beds near Denver, Colorado. The writer does not know on what the determination 

 was based; but it appears probable that the specimens belonged to A. beecheri. 



Aspideretes fontanus sp. nov. 

 Test-fig. 648. 



From the Laramie beds at Ojo Alamo, San juan County, New Mexico, Mr. Barnum 

 Brown, of the American Museum of Natural History, in 1904, brought materials belonging 



apparently to 3 species of the 

 genus Aspideretes. Of these the 

 present is represented by nearly 

 the whole of the right half of the 

 nuchal and a considerable part of 

 the right first costal. The number 

 of the specimen is 6070. 



At no point does this piece of 

 nuchal come to the midline; hence 

 we can not determine the exact 

 extent of the bone laterally. It 

 was, however, not far from 260 

 mm. The animal was therefore 

 one of considerable size. The 

 inner hinder angle of the bone 

 presents a part of the sutural bor- 

 der for the preneural, and from 

 this to the outer end of the nuchal 

 is 125 mm. The width of the bone, 

 where it came into contact with the preneural, is 60 mm. The anterior border is not beveled, 

 but is cut off nearly at right angles with the upper surface. The greatest thickness, thru 



Fig. 648. Aspideretes fontanus. XL Part of nuchal and part 

 of first right costal of type. 



