AND AVES OF NORTH AMERICA. 



LABYRINTHODONTIA Vera. 



Vertebral centra osseous; no branchial hyoids; teeth with much inflected enamel, 

 anchylosed in shallow alveoli. Occipital condyles. 

 Our knowledge of these forms is as yet in many cases too incomplete, to enable us to 

 assert positively as to the structure and position of the teeth, and the preceding arrange- 

 ment is designed to shadow out the true system, rather than to define the groups exactly. 

 They may be arranged further in the following manner, with reference to the dermal 

 armature. 



I. Three large pectoral plates. 



« Abdomen with numerous short or long bony scales in close series. 

 P A bony sclerotic ring. 

 Teeth simple. Xenorhachia. Amphibamus. 



Teeth complex. Ganocephala. Archegosaurus. 



PP Xo bony ring. 



Colosteus n. gen. 

 Pholidogaster. 

 Pteroplax. 

 Microsauria. Ceraterpeton. 



Urocordylus. 



II. Xo pectoral osseous shields. 



a Abdomen with oblique series of long or short scales. 



Microsauria. Sauropleura. 



Otocephalus. 

 Lepterpeton. 

 Ophiderpeton. 

 Hylonomus. 

 Dendrerpeton. 



aa Xo abdominal scales known. 



Pelion. 

 Molgophis. 



XENORHACHIA. 



This order I proposed for the reception of the genus Amphibamus Cope, in 1865. I 

 proposed to regard as one of its characters, the existence of opisthoccelian vertebra?. Such 

 impressions were observed in the matrix in which the fossil was preserved, as to induce a 



