128 



THE PERMO-CARBONIFEROUS RED BEDS OF 



anterior half of the skull. The clavicles were large and plate-like, and formed 

 some protection to the thorax. The vertebral column, composed of very thin 

 intercentra, pleurocentra, and neurocentra, with a very large inner space 

 for the notochord, must have been very weak and very flexible. The propor- 

 tions of the limbs are unknown, but any bones which can be assigned to the 

 limbs of the genus are relatively short and weak, with poorly developed ends 

 showing the presence of a large quantity of cartilage in the joints. It is 

 probable that the carpus and tarsus were also very weak, with few of the 

 bones ossified. We must think of this animal as probably slender, soft- 

 bodied, and salamander-like, with weak limbs and perhaps rather elongate 

 feet. The last idea is suggested by the probability that Tr inter orhachis was 

 largely aquatic, and progressed by swimming. 



It probably lived in very much the same surroundings as the modem 

 mudpuppies, and probably had very similar habits. Large individuals may 

 have reached a length of i meter, but most of the skulls recovered indicate 

 a smaller size. 



Zatrachys (fig. 15). — Known only from the skull, this genus can not 

 be restored, nor very fully discussed, but certain peculiarities of the skull 

 demand comment. The development of processes 

 on the edges of the skull, forming a sort of coarse 

 serration of the periphery, except on the anterior 

 end of the nose and the middle of the posterior 

 edge, is perhaps associated with the peculiarly com- 

 plex natiu-e of the cranial suttires. The midline of 

 the skull is depressed and there are deep pits in 

 front of each orbit, which probably lodged some 

 sensory gland in life. The nostrils are far back from 

 the anterior end of the skull, and the space between 

 and anterior to them is pectdiarly fiat. Broom has 

 recently recorded his opinion that there is a median 

 opening in the anterior end of the skull as in Tre- 

 matops. While we can hazard no guess as to the 

 form of Zatrachys or its habits, we may be sure 

 that it was a highly specialized type, and was perhaps reaching that stage of 

 its development where approaching decadence is heralded by a development 

 of spiny processes. It may be a terminal member of some one of the many 

 branches of the great phylum to which Trimer orhachis belonged. 



Dissorophus and Cacops (figs. 16 and 17).— The first is the most special- 

 ized of the three similar genera which are united in the family Dissorophidcs. 

 All of them have a more or less complete dorsal armor composed of the ex- 

 panded distal ends of the neural spines, alternating in position with overlying 

 dermal plates. In Cacops and Alegeinosaurus, the armor was limited to the 

 midline of the back, and does not descend upon the sides of the body. In 

 Dissorophus the plates are longer, and came well down over the sides of the 



Fig. 15. — Restoration of the head of 

 Zatrachys microplhalmus Cope. 

 About one-half natural size. 



