49 6 



FOSSIL TURTLES OF NORTH AMERICA. 



The sculpture of the carapace is best displayed toward the free borders. It consists of 

 abruptly sunken pits, of which there are usually 5 in a line 20 mm. long. Closer to the free 

 borders the pits are smaller. Nowhere does there appear any tendency for the formation of 



straight rows of pits, such as 

 are seen on the costals of 

 Amyda cariosa, of the New 

 Mexico Wasatch. On the por- 

 tions of the carapace near the 

 midline the pits are less con- 

 spicuous. They appear to be 

 as large, but the walls appear 

 worn down. 



The hvpoplastron (fig. 650) 

 is thick and heavy. At the 



.. .... V 1 r suture with the hvoplastron, 



FIG. 6<;o. Aspideretes austerus. Xs- Right hvpoplastron o) type. r .- , J .,',. , 



r b j> r :r not lar f rom tne midline, the 



thickness is 13 mm. One border of the notch for the process of the xiphiplastron remains. 

 This bone was articulated with the hypoplastron by a jagged suture and it must have extended 

 anteriorly near the midline. The outer end of the hvpoplastron, near the bases of the lateral 

 processes, is 16 mm. thick. 



Evidently nearly the whole lower surface of the plastron was covered by the sculptured 

 layer. The pits are smaller than those of the carapace, there being about J pits in a line 20 mm. 

 long. Many of them coalesce to form winding furrows. 



This species differs from A. fontanus in having a narrower nuchal, much thicker bones, 

 and a considerably coarser sculpture. It is referred to Aspideretes provisionally. 



Aspideretes vorax sp. nov. 

 Text-fig. 651. 



This species was collected from the Laramie deposits near Ojo Alamo, San Juan County, 

 New Mexico, in 1904, by Mr. Barnum Brown. The type is in the American Museum of Nat- 

 ural History and has the catalog number 6140. The species is represented, as far as known, 

 by only the nuchal bone; but this is complete. The length of the bone, from side to side, is 

 200 mm. in a straight line, 215 mm. over the curve. The lateral convexity is considerable and 

 appears to have been somewhat greater than that of either A . austerus or A . fontanus, both 

 from the same locality as this species. The width at the midline is 45 mm., the greatest width, 



55 mm. The greatest thickness is 

 15 mm. There is a moderatemedian 

 sinus in the anterior border. This 

 border is not dipt off at a nearly 

 right angle with the upper surface as 

 in the two other species mentioned 

 above; but is beveled down on the 

 upper surface of the bone to a sharp 

 edge. This beveled surface is not 

 sculptured. The hinder border of the bone presents a median excavation, for the preneural 

 bone. The latter bone was evidently unusually broad, the excavation having a width of at 

 least 55 mm. The preneural border is thicker than that of A. fontanus, the thickness 

 being y mm. 



The sculpture of the bone is obscured by a layer of hard matrix; but so tar as can be 

 determined, it was intermediate between A. fontanus and A. austerus, approaching more 

 closely the lattei 



Certain fragments of costals present probably belong to this species, but possibly to A. 

 fontanus. One of these, apparently the right sixth, is 35 mm. wide at the neural border, 

 30 mm. wide more distally, and has a thickness of 8 mm. 



This species differs from ./. fontanus in having the free anterior border of the nuchal 

 beveled, the bone thicker at the preneural border, and a coarser sculpture. From A . austerut 



Fig. 651. -Aspid, 



eretes vorax 



Nuchal bone of type. 



