MORPHOLOGICAL REVISION II5 



A small humerus, of different form from that of Trimerorhachis, is 

 provisionally referred to Zatrachys. The two ends are nearly parallel. The 

 proximal articular ends are deeply excavated and without condyles. The 

 proximal face descends a considerable distance on the inner edge of the bone. 

 There is little resemblance between this humerus and that of Eryops. The 

 only process on the shaft is a slender ectepicondylar process, and the entepi- 

 condylar process is not large. The humerus is 41 mm. long. 



Genus DISSOROPHUS. (Plate 13.) 

 Dissorophus multicinctus Cope. 



Characteristic Specimens: Nos. 4593 and 4343 Am. Mus. Nat. Hist. 

 Cope Coll. and No. 648 University of Chicago. 



It has been shown in the systematic revision that Otoccelus is indis- 

 tinguishable from Dissorophus. The condition of the skull is very poor, but 

 enough can be made out to show that it has complete temporal fenestrse 

 crossed by a slender plate or bar of bone dividing it into two halves. This 

 character was made out by the author in the type skull. Later discoveries 

 by Williston (73), in the summer of 1909, have confirmed this character and 

 have added much to our knowledge of the skull and carapace. The following 

 description is largely drawn from Williston's description, but there is some 

 additional matter and some corrections. 



The skull: "The skull is very broad posteriorly, with a rounded, obtuse 

 muzzle. The orbits are situated about midway in its length; they are rather 

 small, nearly circular in outline, and broadly separated. The table of the 

 cranium, back of the orbits, is rather broader than long, a little wider anteri- 

 orly, with a broad emargination behind; it is nearly plane, with its margins 

 elevated. The parietal foramen is situated a little back of a line drawn 

 through the posterior margin of the orbits. Just back of each orbit there 

 is a distinct depression, as in Cacops, apparently for the lodgment of some 

 gland. In the middle part behind there is, on each side, a prominent, 

 nearly hemispherical elevation, deeply impressed with large pits; they cor- 

 respond to the prominent rugosities of the Cacops skull, but are much more 

 rounded and less angular. Behind, these swellings are partly separated by 

 an angular emargination of the hind border. The epiotic region on each 

 side is produced backward considerably beyond the transverse line of the 

 rounded swellings. The broad surface between the orbits is shallowly con- 

 cave transversely. The thickened upper margin of the orbits is nearly hori- 

 zontal to the middle of the orbit in front, where there is a rugosity, the outer 

 border of which is nearly vertical. The face in front of the orbits is convex, 

 with a depression on each side in front of the orbital rugosity. The nares 

 are large, oval in outline, and are directed upward and outward and forward. 

 Below and a little behind the orbits there is a distinct elevation or rugosity. 

 The posterior lateral or temporal region is unfortunately wanting on each 

 side, or rather the parts were so mutilated that they could not be joined. 

 The structure here is quite surely, as in Cacops, the epiotic prolongation with 

 its attached quadrate inclosing the ear opening at the bottom of a cavity. 

 The upper margin of this opening is preserved in part on the left side, as 

 is also most of the smooth bone forming the anterior part of the auditory 

 cavity, the ridge limiting this surface from the roughened exterior of the 

 side of the skull in front of it running downward and backward from a point 

 about 10 mm. back of the orbital margin, to the jugal border. 



