A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 7 



A new species of Clepsydrops, C. limbatus, is described from Texas. It is based on 

 a vertebra with the following dimensions : 



M. 



Length of centrum 0.031 



vertical 0.039 



Diameter of centrum 



transverse 0.033 



In the May number of 1878 of the American Naturalist, published April 22, Cope 4 

 made some remarks about the homology of the chevron bones. He says : " The basal 

 portions of the chevron bones are continued throughout the greater part of the vertebral 

 column in the Permian genera Clepsydrops, Metarmosaurus and Epicordylus [Eryops], 

 forming intervertebral elements to which I have given the name inter centra " — " The 

 free elements of the cervical series of some reptiles are probably the same." Here the 

 name intercentrum is introduced. In the same number of the Naturalist Cope 5 refers to 

 Clepsydrops : " Clepsydrops has been found to have the canine and incisor teeth distinctly 

 characterized. The ischia are immensely enlarged in an antero-posterior direction, form- 

 ing a boat-shaped body.* The neural spines of the lumbar and sacral regions are greatly 

 elevated, indicating a fin like that of Basiliscus." Two new species are described, C. 

 natalis and C. gigas, the latter of the size of the larger Mammalia. 



In May, 1878, a paper by Prof. O. C. Marsh 6 appeared in the American Journal 

 of Science on Permian fossils. In the beginning he states that " hitherto no Permian 

 vertebrates have been identified in this country, although not uncommon in Europe." 



He continues : " The Museum of Yale College contains an extensive series of Rep- 

 tilian remains belonging to a peculiar lacustrine fauna, which includes also Amphibians 

 and Fishes. These fossils are from several localities in the West, but mainly from New 

 Mexico, and the geological horizon appears to be in the upper portion of the Permian. 

 These Reptilian remains are in excellent preservation, and among them are several genera 

 having the more important characters of the Rhynchocephalia, of which the genus Hat- 

 teria, of New Zealand, is the living type. The principal points of agreement are the 

 separate premaxillaries, the immovable quadrate, and the biconcave vertebrae. Another 

 character of much interest is the presence of certain hypaxial elements of the vertebras, 

 first observed by Von Meyer in the Triassic genus Sphenosaurus, and called by him inter- 

 central bones (' Zvvischenivirbelbein'). These wedge-shaped bones are apparently the 

 homologues of the cervical hypapophyses in the Mosasauria, and of the subcaudal attach- 

 ments in the Odontornithes, and a few recent birds. These intercentral ossifications 

 apparently exist in all the Reptilia yet found in this new fauna, and hence serve to dis- 

 tinguish it. With this character is another of hardly less interest. The anterior rib- 

 bearing vertebras preserved have three separate articular facets for the ribs, one on the 



*This pelvis probably belongs to Eryops. 



