182 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 83 



Family TRIONYCHIDAE 



ASPIDERETES OVATUS, new species 



FiGUKE 15 ; Plate 18, Figure 1 



Type. — U.S.N.M. no, 12986, consisting of the carapace lacking a 

 portion of the anterior border and fragmentary parts of the plas- 

 tron. Collected by C. W. St<?rnberg, 1929. 



Type locality. — 7 miles northwest of Brimhall's Store. San Juan 

 County, N. Mex. 



Horizoii. — Kirtland formation, Upper Cretaceous. 

 Description. — The specimen selected as the type lacks the nuchal 

 and portions of the right first costal, but otherwise, although much 



checked and slightly 

 distorted, the carapace 

 is quite complete. 



The carapace is oval, 

 with the broader end 

 forward of the middle. 

 The rear end is broadly 

 pointed. The shell has 

 a greatest estimated 

 length of about 310 

 mm and a greatest 

 width of 283 mm. 



The sculpture of the 

 carapace consists of 

 shallow, rounded pits, 

 separated by ridges 

 whose summits are flat 

 topped. Toward the 

 outer margins of the 

 shell the pits tend to 

 arrange themselves in 

 rows parallel with the adjacent border (pi. 18, fig. 1). In the cen- 

 tral area the pits are irregular in placement and less deeply im- 

 pressed. A second specimen (U.S.N.M. no. 12987), which may be 

 referred to this species, shows the central area to be smooth and al- 

 most devoid of pitting. There are a few spots on the central part 

 of the type, showing a similar condition. A narrow band crossing 

 the outer ends of the costals is free of pitting, as are the beveled 

 ends. The sculpturing is distinctive and will serve at once to dis- 

 tinguish this species from the other Upper Cretaceous trionychids of 

 this region. 



Figure 15. — Carapace of Aspideretes ovatus. Type. 

 U.S.N.M. no. 12086. Nl, N6, Neurals 1 and 6, re 

 spectively. One-fourth natural size. 



