292 CATALOGUE OF THE SPECIES OF TERTEBKATA FOUXD IX THE 



The characters of this species confirm the propriety of my proj)osition that Paii- 

 tylus, Ectocynoclon and Pariotichus are members of a single family which difters from 

 the Clepsydropidae in the overroofing of the temporal fossa.* 



DIMETRODON SPECIES. 



My last account of this genus was jniblished in the Proceedings of the American 

 Philosophical Society, 1880. p. 42. Since that time additional material has enabled 

 me to develop more fully the characters of this singular type. 



Hibs. — In this genus and in I^aosaurus the sacral i-ibs are present as in Batrachia. 

 They are short, and vertically compressed, forming a wedge-like. body. 



Vertebral. — I have at various times described the extraordinary development of 

 the neural spines of the dorsal vertebrse in the genus Dimetrodon, which belongs to 

 the ClepsydropidcTB, one of the carnivorous families of the Saurian order Thei'omorpha. 

 The dentition of these animals is of the most formidable character, consisting of com- 

 l^ressed finely serrate teeth on the maxillary and dentary bones mingled Avith huge 

 conic tusks on the middle of the maxillary anterior end of the dentary, and occupying 

 the entire alveolar face of the preraaxillary. The huge neural spines formed an ele- 

 vated fin on the back. In a medium-sized specimen of Dimetrodon mcisivus, where 

 the vertebral body is 35 mm. in length, the elevation is 900 mm. or twenty and a half 

 times as great. The apex of the spine in this species is slender, and apparently was 

 flexible. Its utility is difficult to imagine. Unless the animal had aquatic habits, 

 and swam on its back, the crest or fin must have been in the way of active movements. 

 Accordingly the spines are occasionally found distorted by union of surfaces of frac- 

 ture. The limbs are not long enough nor the claws acute enough to demonstrate 

 arboreal habits as in the existing genus, Basiliscus, where a similar crest exists. 



Stermcm. — A singular bone which I can only regard as this element accom- 

 panies a fragmentary skeleton of the D. incisious or D. gigas ; and other examples 

 occur with other specimens. 



The anterior two-fifths of the bone is nearly square, and slightly concave above, 

 with three angles, one at each side and one anterior ; the rest contracts posteriorly 

 into a long, narrow, flattened shaft, which constitutes three-fifths of the length. 

 This portion is depressed, so that the transverse section is lenticular. The lateral 

 edges are acute, and without articular facets of any kind. The distal extremity is 

 first grooved, and then fissured, each half terminating in an obtusely narrow apex 

 which is applied to the other half. The surface of this part of the element is longi- 

 tudinally grooved both above and below. 



* See Proceedings Aiiier. Philos. Soc., 1883, p. 031. 



