Il6 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



"On the palatal side of the skull the basioccipital, basisphenoid, and 

 parasphenoid could not be recovered, nor the vomerine portion in front. 

 On the left side the pterygoid and palatine regions are nearly perfect and 

 undistorted, save for the interior border of the nares. The nareal opening 

 is long and narrow, the anterior margin a little in advance of the posterior 

 border of the external opening. In front the external border is very close 

 to the dental margin; behind, it is removed a few millimeters. Near the 

 posterior margin of the opening there is a single large tooth, as in Cacops, 

 and doubtless there was another on the vomers at the anterior inner border; 

 no other palatine or pterygoid teeth are visible. The infratemporal opening 

 between the pterygoid and jugal margin is shorter and narrower than in 

 Cacops, and the lateral process, doubtless corresponding to the transpalatine, 

 is smaller. The basisphenoid process of the pterygoid is stout, transverse, 

 and nearly horizontal. Evidently the structure throughout of the palatal 

 surface was quite alike in the two genera. Parts only of the walls of the 

 rhinencephalic chamber are preserved. 



"The maxillary teeth, which extend backward to opposite the begin- 

 ning of the infratemporal opening, are all very small and are much more 

 numerous than in Cacops; I count about forty-five in each maxilla. Those 

 preserved entire are scarcely more than 2 mm. in length. 



"The mandibles, which, with the exception of the extreme anterior end, 

 are preserved complete, are, like those of Cacops, slender bones, deepest 

 immediately in front of the cotylus, with a relatively high coronoid process, 

 which fitted into the infratemporal fossa. I count about thirty-five teeth 

 in each dentary, as preserved. The external surface, at least posteriorly, is 

 closely impressed with circular or oval pits, like those of the cranial table." 



The carapace of the Dissorophides differs materially from that of the 

 Aspidosaurida. This point was not appreciated by Williston, who placed 

 the genus Aspidosaurus, with query, in Dissorophida, and also suggested 

 that the genus Alegeinosaurus was probably synonymous with Aspidosaurus. 

 In the Dissorophidee the dermal plates overlie the expanded neural spines, 

 but are not united with them. In the Aspidosauridee the armor is composed 

 of the expanded neural spines alone. A cross-section of the dermal armor in 

 the New York specimen shows that from the center of the expanded neural 

 spine a strong process runs forward and lies in a groove on the upper surface of 

 the next preceding vertebra. Figure 45 illustrates the characters of the genus 

 as shown in the type specimens of Dissorophus and Otocoelus. The following 

 discussion of the carapace and axial skeleton is taken from Williston (73) : 



" Carapace: The carapace, as preserved, is of essentially the same char- 

 acter as that of Cacops, but of a far greater development. In the series, 

 as adjusted, there are indications of twelve or thirteen vertebrae participating 

 in the shield and others possibly are lost. The whole number may have 

 been the same as in Cacops aspidephorus, that is, fifteen, but I suspect there 

 were more. The first dermal shield, covering three or four vertebrae, appears 

 not to have been intimately associated with the spines of the vertebrae. It 

 is very large, not much broader than long, and heavy. Its front border is 

 very obtusely angular in the middle, with the borders receding and rounded. 

 The lateral borders are subparallel and gently convex in outline. The 

 posterior border has a gentle emargination in the middle with the lateral 

 sides slightly convex behind. The planes of the sides have an angle of nearly 

 forty-five degrees with each other and are broadly rounded in their union. 



