AND AYES OF NORTH AMERICA. 



1 65 



and with external angles less than a right angle. It marks the proximal third of the costal bone. The posterior is 

 truncate behind; the pygal is considerably longer than broad. 



Proximal halves of the two first oostals, wit h the costal crest for the first pair of ribs, are preserved. The suture 

 for the first vertebral bone is little concave. The inter-vertebral dermal suture crosses it, just anterior to the point 

 opposite to the completed capitulum of the bone. 



The xiphisternal, besides being much thinner relatively than that of Taphrosphys molops, is of different form; 

 while its hyposternal suture forms nearly a right angle with the common suture; in the hitter species, an acute angle. 

 The pubic sear in P. sulcatus is of nearly the same length, but much narrower and less elevated. This I have ob 

 served in five specimens. The posterior lobe of the sternum is deeply emarginate. The pubic scars in both converge 

 slightly anteriorly. 



The second specimen, above mentioned, furnishes portions of marginal bones and sternal bridge. The latter pre 

 sented an obtuse angle between the lateral and inferior planes. It also possesses the mesostemal, somewhat broken 

 Its external angle is considerably more than right, and indicates a, thin bono considerably longer than wide, and more 

 like that of P. leslianus than any other species of the genus. 



Measurements of Spec. No. 1. 

 Length of ante-penult costal bone, 

 Width " proxlmally, 



distally, 

 " penultimate proximally, 



" posterior vertebral, 



" posterior COStal proximally, 



" " distally. 



Length of " 



" iliac scar, 



" rudimental costal, 



" caudal marginal, 



" suture between posterior pair marginal seutal, 



Width of caudal marginal, 



This is a species of considerable size. The fragments originally described by Lcid.y are three united marginals 

 from the position of the; sternal bridge. They show that these elements have a thin junction with both plastron and 

 oarapace, and are not separate from the latter, as one might be led to suppose. 



The marginals near the bridge have a fiat and broad inferior surface, and are produced into a- narrow slightly 

 recurved margin, while the tree marginals have the external faoe plane— not recurved— and the internal thickened a 

 line within the margin. 



What is probably a nuchal margin (from Bamesboro, Professor Cook's Collection) is not thickened within, and 

 has, as in other genera, a, much greater transverse extent posteriorly than at the margin. Its form is as follows: 

 Length, 2 in., 8 lin. ; Width, 2 in., 6.5 liu. A peculiarity in the dermal markings is 

 that there is no nuchal scutum, but a suture as in the caudal marginal bone. 



Two marginal hones, having the sculpture characteristic of this species, appear 

 to be referable to it after comparison with specimens in the Museum of the Academy. 



One, a median posterior, is considerably shorter than the other, probably a posterior 



or lateral, a peculiarity not seen among living species. The latter has a thin edge. 

 is thickened along the line of the lower two-fifths the diameter, and then thins out to 

 the upper suture, which is only .1.5 lines wide. 



In. Lin. In. Lin. 



Width of lateral plate, ;i (1.5 Length ot caudal, 2 7. 



Length " :S 4.5 Width " 2 8. 



These plates ace crossed in the usual manner by the sutures of the marginal and costal scuta. 



the Birmingham pits. 



AMBRI. PII.1LO. S00. — VOL. XIV. — 42 



In. 



Lin. 



7 



9. 





30. 



2 



7. 





15.5 





14.5 





13. 



2 



4. 



4 



!). 



:s 







7. 



2 



It). 





11). 



2 



7.5 



Fig. 45. 



r 



V 



•\ 



L 



i 



They are all from 



