BAENID^E. 



97 



Thescelus rapiens sp. nov. 

 Figs. 91, 92. 



This species is represented by a single shell, which was collected from Laramie deposits, 

 .11 < )jo Alamo, San Juan County, New Mexico, in 1904, by Mr. Barnum Brown, of the 

 American Museum of Natural History. The catalog number of the specimen is 6066. 

 The shell has been damaged considerably by weathering, and lacks a portion of the carapace 

 in the nuchal region, some portions of the right costals, most of the peripherals, the front of the 

 plastron, and the rear of the xiphiplastrals. 



The length of the carapace must have been close to 400 mm.; the width about 375 mm. 

 Apparently the shell was considerably deprest. The front of the carapace over the neck was 

 excavated, but not so deeply as in T. insiliens. The area occupied by the vertebral scutes 

 presents a broad, shallow longitudinal channel; but in this, over the neural bones, there is a 

 low ridge. The free borders of the anterior peripherals are rather obtuse. 



The sutures of the shell are obliterated, but a few of them may be traced by the fine stria- 

 tions which cross them. So far as they can be made out, they are shown in the diagrammatic 



92. 



I H.s. 01 and 92. Thescelui rapiens. Carapace and plastron. Type. Xj. 

 91. Carapace. 92. Plastron. 



figures. The scutal areas are distinctly markt on the shell. They present various irregularities. 

 The vertebrals (fig. 91) are broader than long; their dimensions are shown in the table 

 on page 98. 



On the left side there is a supernumerary costal scute. This has been cut off" mostly from 

 the first costal proper, but to some extent from the second marginal. The fourth marginal, 

 shown on the left side, has a height of 57 mm., rising somewhat on the costals. 



The plastron (fig. 92) is large. From a low ridge which joins the free border of the front 

 lobe with that of the hinder lobe the bridges ascend at an angle with the remainder of the 

 plastron. The axillary notch is far forward,' falling about 55 mm. behind the front of the 

 carapace. The opening for the head and legs is thus considerably restricted. The front lobe 

 extended evidently much bevond the front of the carapace. Its length can not be determined. 

 7 



