140 MEMOIRS OF THE CARNEGIE MUSEUM 



In a straight line the shell has a greatest estimated length of 135 mm. ; at the 

 center a greatest width of 115 mm. Though depressed, the upper shell is broadly 

 convex in all directions, dropping off rather more rapidly toward the back than 

 toward the front. The upper surface of the carapace is smooth, the sulci lightly 

 impressed, and nowhere are scutal growth lines to be observed. 



Fig. 16. Carapace of Echmatemys depressa. Type. C. M. No. 2936. One-half natural size, c.p.', 

 c.p. S, costal plates one and eight; nS, n7, neurals two and seven; nu.p., portion of nuchal plate; pij, pygal; 

 spy, suprapygal; v.s. 2, second vertebral scute. 



The nuchal is onlj^ partially preserved, but this portion shows that it had a 

 greatest width of 26 mm. and was obtusely keeled at the center. The anterior 

 border, as shown in Fig. 16, is missing. 



There are eight neurals, all of which are hexagonal, with the exception of the 

 first and eighth, the latter being subrectangular in outline. All have their antero- 

 lateral angles truncated, which serves at once to distinguish this form from Ech- 

 matemys pusilla Hay, which has the postero-lateral angles of the neurals truncated. 

 The neurals gradually decrease in size from front to back, and, excepting the first 

 and third, all are broader than long, as shown in the accompanying table. The 

 second and third neurals are sharply keeled on their posterior and anterior ends 

 respectively, as are the fourth and fifth, while the sixth, seventh and eighth are 

 keeled their entire lengths. The keel on the suprapygal is very low and hardly 

 discernible. 



All of the costals of the right side are present and perfectly preserved. They 

 are of moderate thickness with pointed distal ends which articulated with the periph- 

 erals by gomphosis. Portions of the buttresses preserved in the matrix indicate 

 that they articulate with the costals considerably above the costo-peripheral suture. 



