130 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



expansion, bounded inwardly by a sharp sinuous crest, which becomes con- 

 fluent with the convexity of the distal extremity. 



"fibula (plate 23): The fibula is shorter than the tibia, flattened upon 

 its posterior inner surface, and convex from side to side on the opposite. 

 The outer thinner margin is nearly straight to the lower fourth, where it 

 curv^es inward. The inner border is deeply concave, more so on the lower half. 

 The lower extremity is more expanded than the upper, and is also thicker, 

 strongly convex in front, and somewhat concave on the posterior surface. 

 In the vertical position of the bone the upper articular surface is nearly hori- 

 zontal, while the lower is directed at an angle of about 20 degrees inwardly. 



"Associated with the leg bones were found a number of tarsal and pha- 

 langeal bones, figures of which will be found in plate 21, figs. I and 2. Their 

 precise position can not be determined, more than that two of the tarsals 

 belong in the proximal row and three of the toe bones are metatarsals." 



Family TREMATOPSID^ Williston (page 66). 

 Genus TREMATOPS Williston (page 67). 

 Trematops miileri Williston (page 67). (Plates 14-16.) 



Characteristic specimen : No. 640, University of Chicago. 



The morphological description here given is a reprint of Dr. Williston's 

 original article (71). 



"Skull: The skull of Trematops is remarkable, not only among amphib- 

 ians, but also among Permian vertebrates, for the association of certain 

 peculiar characters, widely distinguishing the genus from any other now 

 known. The chief of these characters are: the possession of a median, 

 unpaired rostral opening leading into a palatine vacuity; greatly enlarged 

 antorbital vacuities; a temporal fenestra; and the apparent absence of the 

 parasphenoid bone of the palate. In the skeletal characters, aside from 

 those of the skull, the genus does not differ much from Eryops, so far as 

 known, and doubtless the skeletons of each, when fully known, will show 

 a like agreement throughout. 



"In shape the skull is subtriangular, its width posteriody being but 

 slightly less than the length from premaxillae to occipital condyles. Its sur- 

 face is coarsely and rather deeply pitted, but presents no traces of mucous 

 canals that I can distinguish. The face is markedly constricted just in front 

 of the orbits, the facial region showing a slight lateral convexity on the outer 

 sides of the large antorbital vacuities. Back of the orbits the 'table' of the 

 skull is broad and neariy flat, perforated by the rather small parietal fora- 

 men near its middle. The orbits are oval, their greater diameter oblique 

 to the longitudinal axis of the skull, their borders thickened in front and 

 behind, but thinner above and below, with the plane of their margin look- 

 ing obliquely forward, upward, and outward. Immediately back of the orbit 

 at its outer part, the table turns downward, forming the anterior bar of the 

 temporal vacuity. The upper margin of this vacuity is perfectly preserved 

 on the left side, but the fragments forming it were not recovered for the 

 right side of the skull. It is thinned, in outline gently concave and turned 

 outward, and, posteriorly, a little downward, forming the lateral margin of 

 the flat table of the skull. The natural character of the border is_ beyond 

 dispute, the small pittings of the surface continuing quite to the junction 

 of the upper with the lower surface of the cranial bones. There is no possi- 



