Shull of Mochlorbiniis platyceps. 1S5 



affairs long-continiied usage justifies and establishes a title ; 

 and since nomenclatare is a m^itter of coaTetiienee, it is a mica 

 point whether the unchallenged ose of Ovren's name for a long 

 time has given the reptile a preference over the crastacean. 



Professor Cope, in 1S70, withoat apologrfy proposed the 

 name Lystrosaurus for a Soath-Africaa fossil from which he 

 drew manj of the characters of the skull ia detming the 

 Dicynodontia. When this specimen was accttrateljr figxiired 

 in 1892 it proved to be a typical example of Pty(:ho'jnathus. 

 If that name should be eTentaalijr withdrawn from the Soatrh- 

 African fossil, Lysfrosaunis is the only name which coald 

 take its place, as Professor Cope ha- j /" : Zittel and others 

 have continued to xxbq the name t :ms. 



In 1889 Mr. Lvdekker discarded FLtfcho^naikHS and adopted 

 in place Ptychosiagxim, a new name appHed by Mm to the 

 Indian fossil from the Panchet rocks in the Lower Gromdwana 

 series, which Profess<3r Huxlej referred to Dicynodanj which 

 may be conveniently retained for that type. The Indian 

 specimens appear to differ in the shoulder-girdle, humerus, 

 vertebrae, and all known parts of the skeleton fr?m the 

 remains of Ptychognathus^ which are only obta.. ' "l tie 

 Upper Karroo rocks of South Africa, while .! . ;-* is 

 only known from the Middle Karroo series. No entire skull 

 of the Indian genus is recorded, and there is no evidence that 

 it has the generic character of a ironto-nasal angle in the 

 skull which distinguishes Ptycht^nathus from Dicynodo'n. 



The determination of the generic name is important be- 

 cause there are some allies of Ptychognathits which appear to 

 show that it indicates a small family of S-JUth- African reptiles 

 distinguished by the way in which the brain is elevated 

 above the floor of the brain-case as it extends forward. This 

 difference from some types of I>ieynodo'n is ci^mparable to 

 that seen in modern crocodiles, in which the front of the brain 

 is supported upon a median plate, while in Teleosaars it rests 

 upon the basicranial bones. 



The subgeneric modifications which have come under ray 

 notice are two in number — tirst, a skull having a narrow 

 longitudinally channelled cerebral region, with outwardly 

 inclined sides, unlike the table-headed type of Ljfstr&sawrms ; 

 and, although the straight face makes an _ '.end with 

 the roof of the head, the surtaces are not pcii : -;i angular 



ridge, but round into each other. That genus may be named 

 Ehabdotocephalus J with the type B. Jficcatgi. A second sub- 

 generic form named Mochlorhinus is dLstinguished from the 

 type Lystrosaurus by the perfect rounding of the face into 

 the flat table-top of the skoli, coupled with the development 



