AND AVES OF NORTH AMERICA. 61 



is perhaps a posterior dorsal. It is but slightly curved, has a vertically broad oval section proximally, and a depi eased 

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



M. M. 



Length, 0.23 Vertical diameter at distal third, 0.014 



Do. from head to tubercle, 0.03 Transverse do., 0.153. 



I find no abdominal ribs, such as are abundant in the North Carolina specimen described on a pieceding page. 



This species has been distinguished from B. priscus by the form of its caudal vertebra. The measurements given 

 by Emmons and Leidy, 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 articular 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, as furnished by.Cuvier. This would give to the Belodon lepturus a length of about ten feet, and a 

 habit stouter 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 Phoenixville, Penna. 

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

 ing Railroad. This stratum is, according to Wheatley, ft. 6 in. from the top of the series; 52 ft. 6 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, prootic 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 Sternothaerus, 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 procoelian, i. e. with anterior cup and posterior ball; the sphenoid bone 

 little visible on the base of cranium. 



PROCOELI. 



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

 more horizontal exposure on base of cranium. 



AMPHICOELI. 



The only genus of Amphicceli known in this country is Hyposaiirus ; the Procoelian 

 genera are the following: 



A The teeth composed of several enclosed cones of dentine. 



« The cervical vertebras 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. 



THORACOSAURUS. 

 AMERI. PH1LOSO. SOC. — VOL. XIV. 16 



