AND AVKS OF NORTH AMERICA. 



61 



Is perhaps a posterior dorsal. It is but slightly ourved, has a vertically broad oval section proximally, and a depressed 

 trigonal one distally; there is little trace of a, medullary cavity. 



M. M. 



Length, 0.3:! Vertical diameter at distal tin id, 0.014 



Do. from head to tubercle, 0.03 Transverse do., 0.155. 



I find no abdominal ribs, sueb as are abundant in the Nortb Carolina specimen described on a, preceding page. 



This species has been distinguished from 1!. priscus by the form of its caudal vertebrae. 'Plus measurements given 

 by Emmons and Ijeidy, of the other species, differ in the greater elongation of the vertebral centra. The length of 

 the latter is in each case greater than the width of the artioular face, instead of less. They are also smaller in all 

 their dimensions. We shall not go very far wrong in estimating the length of this species on the basis of the gavial 

 of the Ganges, ;>.s furnished by Cuvicr. This would give to the Belodon lepturus a length of about ten feet, and a 

 habit stonier than that of the Crocodiles of the present day. 



This species was discovered by Chas. M. Wheatley, proprietor of the lead and zinc mines at Phomixville, Penna. 

 He obtained the remains from the "Bone bed" of the Trias, where exposed by flic Tho-nixville Tunnel of the Read- 

 ing Railroad. This stratum is, according to Wheatley, (i ft. in. from flu; fop of flic series; 52 ft. (i in. lower down 

 is a stratum rich in plants and Saurian remains, and 95 ft. deeper occur bituminous shales with caprolites and bones. 



CROCODILIA. 



The constitution of the cranium in this order is very characteristic and peculiar. The 

 basal cranial bones are forced backwards, so that they occupy a more or less vertical posi- 

 tion, and the sphenoid is almost concealed in many. The quadratum is immoveably 

 embraced by the exoccipital, proiitic and opisthotic. The pubes do not enter into the 

 walls of the acetabulum as in Mammalia and Reptilia, but originate from the inferior 

 pelvic arch. They form no common suture, but extend sub-longitudinally, thus differing 

 from pubes generally. The latter relation of true pubes occurs among Reptiles only in 

 Chelys, Pelomedusa galeata, and Sternothserus, among the Chelonia, and in Pterosauria. 

 An anterior process from the ischium occupies the usual position of the origin of the 

 pubis, as a support for the latter. 



There are at least two well marked types in the class, defined as follows: 



Vertebrae procoeHan, i e. with anterior cup and posterior ball; the sphenoid bone 



little visible on the bast; of cranium. 



PEOCOELI. 



Vertebrae concave or nearly plane at both extremities; sphenoid bone with larger and 

 more; horizontal exposure on base of cranium. 



AMPHTCOEI.I. 



The only genus of Amphicoeli known in this country is llyposaurus ; the ProcoeHan 

 genera are the following: 



A The teeth composed of several enclosed cones of dentine. 



« The cervical vertebree with very rudimental or split hypapophyses. 



A large fossa or foramen issuing between the prefrontal and lachrymal bones of the 

 face; muzzle long, slender, teeth equal. 



THORACOSADRUS. 



AMBRI. PH1L0S0. SOC. — VOL. XIV. 16 



