17 



lar extremity. The latter looks partly downwards, and is divided by a 

 deep groove above into two parts representing the usual condyles. One 

 of these is comparatively depressed, while the other has a massive superior 

 crest, which makes its long axis vertical instead of horizontal, as is that 

 of the other condyle. 



There is considerable resemblance between this femur and that of 

 Dimetrodon gigas, and in a less degree to that of Glepsydrops nalalis, but 

 both the latter have well developed condylar surfaces. They are also 

 larger in proportion to the size of the rest of the skeleton, in the Pelycosau- 

 rians mentioned. 



Further characteristics of this genus and of the species it embraces will 

 be given at a future time. 



TRIMERORHACHIS Cope. 



American Naturalist, 1878, p. 328 (April 22). Proceedings American 

 Philos. Society, 1878, p. 524. 



This genus, as has been pointed out, differs from Eryops in the super- 

 ficial character of its vertebral ossifications, and in the absence of ossified 

 neural spines. 



A well-preserved cranium, and portions of several others referrible to 

 this genus, furnish characters which have beeti hitherto inaccessible. They 

 probably belong to the T. insignis, but this is not certain. 



Generic Characters, etc. — The type of skull is that of the order of Stego- 

 cephali generally. The superior walls are thin, and are sculptured on the 

 superior surface. The mucous grooves are distinct, but do not form a 

 well-defined lj r ra. There is a groove which is parallel to the anterior 

 borders of the orbit for a short distance, and which then turns forwards 

 and then inwards. The dermal ossification is distinguished from that of 

 the maxillary bone by a squamosal suture. A mucous groove descends to 

 it obliquely forward from the superior quadrate region, aud sends a branch 

 at right angles to its anterior extremity to a point posterior to the orbit. 

 Of superficial ossifications, the boundaries are difficult to determine, owing 

 to the obscurity of the sutures. Enough can be seen to demonstrate the 

 presence of supramaxillary, epiotic, and supraoccipital dermal bones. The 

 nostrils are large aud well-separated, and look upwards. 



The teeth are acute, and of subequal size ; their superficial layer is 

 deeply inflected at the base. 



The parasphenoid bone is wide posteriorly, but contracts abruptly, and 

 extends forwards on the middle line. Owing to crushing of a part of the 

 surface, I am unable to ascertain its anterior, or vomerine suture. The 

 basifacial axis bone is quite narrow, and is edentulous. It is connected with 

 the superior cranial walls by a vertical osseous plate on each side, which 

 may represent alisphenoid, orbitospheaoid and ethmoid. The palatoptery- 

 goid arch is a longitudinally extended sigmoid, enclosing with the axial 

 elements, an enormous choanoorbital foramen. It extends from the 

 middle line below a short distance posterior to the position of the nostrils 



