64 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



Table III— Contrasting the Families of the Cotylosauria. 



I. Suborder Diadectosauria. 



A. Diadectidce. 



1. Surface of the skull rugose or tuberculate. 



2. Pineal eye enormous. 



3. Occipital condyle flat or concave. 



4. A more or less complete armor of dorsal plates and plates overlying the ribs. 



5. Anterior ribs, at least, expanded into wide plates. 



6. Body low and heavy; neck extremely short; limbs stout and clumsy 



7. Tail moderately long, with strong chevrons. 



B. Bolosaurida. 



1. Skull smooth or slightly rugose. 



2. Pineal eye small. 



3. Occipital condyle rounded. 



4. No armor. 



5. Ribs not expanded. 



6. Body low; limbs short, not heavy. 



7. Not determinable. 

 II. Suborder Pareiasauria. 



A. Pariotichidce. 



1. Small. Skull rounded anteriorly, flattened, amphibian in appearance. Fine sculpture on the 



bones of the skull. 



2. The basioccipital and basisphenoid united and forming a large plate on the base of the skull. 



?. Incisor teeth not enlarged. One or two cheek teeth anterior to the orbit larger than the rest. 

 More than one row in each jaw. 



B. Captcrhinidce. 



1. Small, but larger than the Pariotichidce. Skull acuminate, rugose. 



2. Basioccipital and basisphenoid small; not forming a large plate on the base of the skull. 



3. Incisor teeth much enlarged, tusk-like. Cheek teeth gradually increasing in size to the middle 



of the series and then decreasing. More than one row in each jaw. 



C. Seymourida. 



1. Skull size of that of Labidosaurus. A large epiotic notch, quadrate exposed but without pos- 



terior hook. 



2. Basioccipital and basisphenoid small; not forming a large plate. 



3. Median incisors not enlarged. Cheek teeth simple cones, none enlarged. More than one row 



in each jaw. 

 III. Suborder Pantylosauria. 



A. Pantylidce. 



1. Slightly larger than the Captorhinidce. Skull cordiform. Quadrate not exposed. Surface 



with a particularly close, reticulate sculpture. 



2. Median incisors very slightly larger than the others. Cheek teeth in the form of blunt, swollen 



cones; the second or third larger than the others. Posterior cheek teeth small. 



3. More than one row of teeth in each jaw. 



Table IV. — Contrasting the Characters of the Genera of the Suborder Diadectosauria. 

 Family Diadectidce. 



Diadectes (in addition to the characters given under the family and suborder). 



1. Middle cheek teeth with three distinct cusps. Number of cheek teeth variable. Tooth line 



sigmoid. 



2. Skull with coarse, rugose sculpture; not tuberculate. 



3. The third, fourth, and fifth ribs expanded into triangular plates. The sixth, seventh, and eighth 



overlaid by slender plates. 



4. Transverse processes of the vertebrae extending beyond the zygapophyses. 

 Diasparactus. (Only the vertebrae known.) 



4. Transverse processes of the vertebrae not extending beyond the zygapophyses. The centrum 

 relatively small. 

 Bolbodon. (Only the skull known.) 



1. Teeth uncertain, perhaps with a single cusp in the molar series. 



2. Skull with finer sculpture; not tuberculate. 



