Class MONOCONDYLIA. 



Subclass REPXILIA. 



The subclass Eeptilia is one of the two into which the members of 

 the class Mouocondylia naturally fall. It is deflued as follows: 



Basicranial axis ossified. Vertebral column consisting chiefly of 

 centra. Limbs of the uonpisciue type, that is, embracing a single proxi- 

 mal element, two propodials, several mesopodials, metapodial, and pha- 

 langeal elements. One occipita Icondyle. A distinct quadrate bone, or 

 suspensorium of the lower jaw. Mandible segmented. Carpal, tarsal, 

 and metapodial elements not coossified with each other. 



Cerebral hemispheres larger than mesencephalon, whose moieties are 

 fully exposed above, and not laterally. Cerebellum small. Heart with 

 three chambers. Aorta derived from two aorta roots, which consist of 

 one or two bows on each side. Lungs cellular, functional. Gall blad- 

 der, pancreas, and fat-bodies present. Integument scaly. Mammary 

 glands, none. 



Reproduction viviparous or ovoviviiiarous. Fertilization internal. 

 Copulatory organs present. Embryo with amnion and allantoisj pla- 

 centa, none. 



The Eeptilia are definitely known to appear in geological time in the 

 Coal Measures, near the close of the Carboniferous system, although 

 they probably appeared earlier during that system. They are repre- 

 sented by a number of orders, which are distinguished as follows : 



I. Quadrate bone united with adjacent elements by suture; temporal regions with 



roof of a few symmetrical segments. No distinct postorbital 

 bars; vertebne amphicoelous ; ilium narrow, vertical; feet ambu- 

 latory COTVLOSAURIA. 



II. Quadrate bone united by suture to adjacent elements; one longitudinal postor- 



bital bar (Synajytosauria). 

 a Scapular and pelvic arches not within thoracic and abdominal bones. 



Paroccipital not distinct; no supramastoid ; vertebric amphiccelous ; 

 ribs with one head on centrum ; the capitulum, when present, inter- 

 central; scapula simple Theromora. 



Paroccipital not distinct, a supramastoid; vertebnu amphiplatyan; ribs 

 with one head, and that not intercentral ; scapula triradiate. 



Plesiosauria. 



Paroccipital and supramastoid distinct; vertebrai with two-rib artic- 

 ulations on centrum; phalanges, carpals, and tarsals of similar 



form ICHTHYOPTEKYGIA. 



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