AND AVES OP NORTH AMERICA. 



'29 



PYTHON OMORPH A. 



Characters of skeleton as the preceding, except : opisthotic distinct, prolonged from the 



cranial walls as suspensorium of the quadratum. 

 No symphysis mandibuli. 

 Squamosal present ; premaxilliary single. 



Cranium with alisphenoid and parietal developed in front of prootic. 

 limbs inflexible, natatory ; sacrum none ; chevron bones. 

 Neural arches not attached to centrum by suture. 

 Pubes and ischia wanting. (!) 



(I I'D I 1)1 A. 



Characters of Lacertilia except : opisthotic free, distinct from the cranium except proxi- 

 mally, supporting quadratum ; no squamosal. 



Cranial cavity largely ossified anteriorly. 



Palatine bones free from other elements except pterygoids. 



No symphysis mandibuli. 



Sternal and pelvic arches wanting; no limbs except rarely rudiments posteriorly; no 

 sacrum. 



Vertebra; united by double articulation ; neural arches continuous with centra; no chev- 

 ron bones. 



Circulatory and Nervous Systems, in important feature's as Lacertilia. 



1 1: II T HTOF T E RTGIA. 



KM LT 1 1 Y OS A II It ITS, (Jonybeare. 



Leidy says with reference to the species here described, "They have an affinity to 

 Ichthyosaurus and Eosaurus, nor am I prepared to prove that they do not belong to one 



of these." 



ICHTHYOSAURUS GRANDIS, Leidy. 

 OJionespondylut yrandis, Leidy. Proo. Acad. Nat. Soi., Philada., 1808—178. 



Humboldt; Co., Nevada. 



AMEltl. PH1LOSO. SOC— VOL. XIV. 8 



