46 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



"Measurements. 



M 



"Width of the skull at the quadrate region 0.038 



Width of the skull opposite the orbits 030 



Projection of the quadrate region beyond the midline of the skull .013 

 Length of the incomplete skull (about .01 or .02 m. missing). . . .052" 



Revised description: This species was founded on a very imperfect frag- 

 ment of a skull. I am unable, with fuller knowledge, to identify it as belong- 

 ing to Trimerorhachis. It must be dropped as indeterminate. Further 

 knowledge may show that the type is a fragment of a skull of the genus 

 Cricotillus Case. 



Trimerorhachis mesops Cope. 

 Proc. Am. Phil. Soc, vol. xxxiv, 1896, p. 454. 



Type: An imperfect skull and a good portion of the vertebral column. 

 No. 4568 Am. Mus. Hist. Cope Coll. From Texas. 



Original description: "The greater part of the skull and vertebral column 

 with ribs and thoracic plates represent this species. The vertebral column 

 and ribs rest in a sheet of matrix whose upturned edges suggest that it con- 

 tains as a support a ventral armature. It also looks like a cast of a cavity 

 left in the matrix by the dissolution of the inferior body wall. The only 

 part of the vertebrae discernible without further cleaning are the neural 

 arches. Limbs not detected. The posterior border of the skull is damaged, 

 but one angle is preserved and all of the other but the apex. The remainder 

 is in good preservation on one side or the other, and the surface has been 

 cleaned by weathering. The lower jaw is tightly closed on the upper. 



"The skull does not expand posteriorly as in the T. insignis. The pos- 

 terior border of the orbit is 4.5 times the diameter of the latter in front of 

 the angle of the mandible, and four times posterior to the line of the end of 

 the muzzle. It is thus nearly in the middle of the length of the skull and 

 posterior to the position it holds in the T. insignis. The interorbital space 

 is nearly twice as wide as the diameter of the orbit, while in T. insignis it 

 equals that diameter. The muzzle is therefore relatively elongate, and it 

 projects an eye diameter beyond the line connecting the anterior borders of 

 the nostrils. The latter are large and look upwards; and the long or antero- 

 posterior diameter equals the transverse diameter of the orbit. There are 

 no preorbital or interorbital depressions. The sculpture is strongly marked. 

 On the jaws it is generally longitudinal; on the supra temporal, radiating; 

 on the top of the front and muzzle, reticulate with some predominance of 

 the longitudinal ridges. The sensory grooves are very obscure, but are 

 traceable on the internal borders of the nostrils, but scarcely posterior to 

 them. The groove on the internal side of the inferior border of the man- 

 dibular ramus is distinct. The rami are more transversely expanded than in 

 the specimens of T. insignis, but some of this may be distortion due to pres- 

 sure. The parasphenoid is narrow for the greater part of the length. 



"The T. bilobatus is known from the angles of the mandible of two 

 individuals, and probably by associated remains. The corresponding parts 

 of the T. mesops are much more expanded transversely inwards, are hori- 

 zontal in fact where the inner wall is, in the T. bilobatus, vertical. The 

 strong internal keel of the latter, if represented at all in the T. mesops, has 

 an external position. 



