A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 33 



In 1880 Twelvetrees 55 discovered a skull and humerus in the same deposits from 

 which the earlier Russian fossils had been taken. The skull was of a Labyrinthodont 

 which he called Platypodosaurus, and the humerus he referred to Owen's Theriodontia. 



In the same year the same author described 56 the genus Cliorhizodon, and two years 

 later, in an article in the Geol. May. 57 described teeth referred to the genera Cynodraco 

 and Deuterosarus. 



In 1876 Owen 58 published a review of the Permian reptiles, in which he discussed 

 most of the Permian forms. 



In 1883 Trautschold 59 described the remains preserved in the collection of the 

 University of Kasan. Two new genera were described, Platyops and Trematina. 



In 1894 Seeley 60 discussed and figured the two principal genera of the Permian 

 deposits of Russia, Rhophalodon and Deuterosaurus. He considered that of all the forms 

 described from this region there are only two types. He says, p. 664 : " The remains 

 with a Theriodont dentition show two generic types, which are indicated by the skulls. 

 They are defined as Rhophalodon (Fischer, 1841) and Deuterosaurus (Eichwald, 1848). 

 Kutorga had previously founded Brithopus on the distal end of a humerus ; Orthopus on 

 the proximal end of a humerus ; Syodon was based on a tooth. Fischer in 1847 

 separated Dinosaurus from Rhophalodon by dental and cranial characters. It is probable 

 that the separation was based on sufficient evidence. And, although there is no con- 

 clusive association of parts of the skeleton to support the reference, it seems to me not 

 improbable that Brithopus is identical with Deuterosaurus. That Orthopus includes 

 /Syodon, and the type of Rhophalodon, while the remainder of Rhophalodon corresponds 

 with the genus Dinosaurus, as conceived of by Fischer." 



These two forms he considers as belonging to the Anomodontia, but constituting a 

 separate suborder described as follows, p. 715 : " The Deuterosauria are defined as 

 Anomodontia, distinguished from the other known groups by having (1) the palato-nares 

 divided by the vomer and without having any hard palate extending over them. (2) 

 The canine teeth are serrated (and large) with incisor teeth in front (in Deuterosaurus) 

 and molar teeth behind. There are temporal vacuities and a pineal foramen. (3) There 

 is no facet for the head of a rib on the (middle dorsal) vertebra?, and no proof that it 

 was attached between any two centra in any vertebra? ; the tubercle is attached to the 

 transverse process. The lower dorsal ribs have no antero-posterior expansion. (4) 

 There are two sacral vertebra? anchylosed. (5) The ilium has a small crest without con- 

 spicuous anterior development. The acetabulum is imperforate, as in the Dicynodontia 

 and the Ornithosauria. The limbs and the shoulder girdle are strong. (6) The scapula 

 is flat. 



The two genera appear to be the types of two distinct families, Deuterosaur'idai and 



a. p. s. — vol. XX, E. 



