AND AYES OF NORTH AMERICA. 27 Opisthotic united with exoccipital ; brain case not closed before proOties ; palatines united all round ; sacrum of two or one vertebra ; pubes transverse. LACEItTILIA. Opisthotic distinct and distally free from the cranium ; brain case partly closed before prootic, palatines united. PYT HONO31OR PH A. Opisthotic distinct, free from cranium except proximally ; brain case nearly closed anteriorly, palatines attached behind only. OPHIDIA. I CHT IIYOPT E RYG I A. Elements of the limbs beyond the humerus not differentiated, in indefinite number. Postorbital and supertympanic bones over the temporal fossa. Quadratum solidly united by suture with the prootic opisthotic and quadratojugal. Sacrum none. Pubes and ischia transverse and in contact. Neural arches free. Premaxillary divided. ARCHOSAURI A. Elements of the limbs, of the pes and mantis differentiated, in definite number. Postorbitals and supratemporals " of Owen w anting. Quadratum immoveably united by suture with opisthotic, prodtic and quadratojugal. Sacrum of from one to six vertebrae. Neural arches attached by suture in most. Premaxillary divided. Cranial walls cartilaginous anteriorly. Palatine bones in contact with maxilliaries, and united by suture with them. Circulatory Syste»z (known only in the Crocodilia). Heart with complete septum of the ventricles ; a communication between aorta roots. Nervous System (known only in the Crocodilia). Cerebellum with small lateral lobes and weak plicae. TESTUDINATA. Parts of limbs differentiated. Donal vertebrae without mobility : no clavicle, a procoracoid continuous with scapula : ilium vertical, acetabultim complete. Sternum not in connection with corticoid, composed at least of eight or more bilateral elements, and extending posteriorly to beneath the pelvis.
