62 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



"Measurements. mm 



" Length of the humerus 54 



Length of the radius 41 



Length of the scapula (approximate) 60 



Length of an anterior dorsal rib 45 



Length of a posterior dorsal rib 35 " 



Revised description: This genus resembles Cacops Williston very closely, 

 but differs in the ribs, which have strong posterior processes overlapping 

 the succeeding rib. Williston (72) has suggested that this genus is a syn- 

 onym of Aspidosaurus, but it is much closer to Cacops. There are dermal 

 plates free from the neural spine, as in the Dissorhophidce, while in the Aspi- 

 dosauridce the dermal armor is formed by expansion of the neural spines. 

 1-6. Mid-dorsal region, only, known. 



7. Dorsal vertebrae with neural spines expanded but not wider 



than the vertebrae. Small dermal plates overlying the neural 

 spines directly, and each overlapping the preceding plate, 

 not wider than the vertebrae. No enlarged anterior plate. 



8. Ribs double-headed, with a long, slender, posterior prolonga- 



tion from a point near the upper end. 



9. Cleithrum present, large, as in Cacops. 



Genus CACOPS Williston. 

 Bull. Geol. Soc. Am., vol. 21, 1910, p. 253. 



Type: A nearly complete specimen, No. 647 University of Chicago. 

 From Wilbarger County, Texas. 



Original description (in addition to the characters of the family Dis- 

 sorhophidcs given by Williston, p. 51): "Dermal carapace but little wider 

 than the vertebrae, narrowed in front and not fused into an anterior shield. 

 Cleithrum thin and more expanded. Scapula less expanded below, the 

 interclavicles and clavicles more slender." 



Revised description: 



1. Small, not exceeding 500 centimeters in length. 



2. Skull not elongate, elevated, resembling in general proportions 



that of Diadectes. Orbits large, looking laterally and up- 

 ward. Otic notch forming a closed fenestra. 



3. Nares near the anterior end but more lateral in position than 



in Dissorhophus. 



4. Parasphenoid, small, almost vestigial. 



5. One tooth on each prevomer and palatine. Maxillary and man- 



dibular teeth small and conical; 22 to 23 in the maxillary. 



6. 21 presacral vertebrae, 2 sacrals, 6 pygals, and 15 to 16 chevron- 



bearing caudals. 



7. Dorsal vertebrae with neural spines expanded, and wide antero- 



posteriorly. Dermal plates overlying and alternating with 

 the neural spines. Narrow laterally, not greatly wider than 

 the vertebrae; no enlarged anterior plate. 



8. Ribs double-headed anteriorly, without posterior prolongation. 



9. Cleithrum present; thin and more expanded. 



10. Scapula less expanded below; the clavicles and interclavicles 

 more slender. 



