PRIMITIVE REPTILES 659 



probability allied to Diplocaulus, while others must be removed 

 from the order. 



But I care not whichever name is applied to the group I here 

 call Microsauria, since in all probability it will be repeatedly 

 changed before a fairly definite conclusion is reached; and that 

 conclusion will not be reached until we know vastly more about 

 the carboniferous vertebrate fauna than we do at the present 

 time. 



If the Microsauria, as typified by the above mentioned genera, 

 are true, or real reptiles, what position in the system should 

 they occupy? The vertebrae are purely holospondylous, and 

 it is the universal belief that rhachitomous vertebrae are primi- 

 tive; to assume the reverse is to rewrite the morphology of the 

 vertebrae, and especially of the atlas of the Amnio ta; nor has 

 there been a shadow of an argument so far produced to disprove 

 the theory. The cleithrum has never been observed in any 

 microsaur, and its presence in the Cotylosauria can only be 

 explained as a direct inheritance from the Amphibia. Since 

 neither the intercentra nor cleithrum could have reappeared 

 after their one-time loss the probability that any known micro- 

 saur could have been ancestrally related to the later reptiles is 

 very slight. If these microsaurs are real reptiles or even indi- 

 rectly ancestral to any modern reptiles, we must of course seek in 

 early rocks their ancestral Amphibia. But we have so far no 

 evidence whatever that Eosauravus and Sauravus may not 

 actually belong among the Cotylosauria, where some authors 

 would place them. It is true the vertebral arches of Eosauravus 

 and Sauravus do not seem to partake of the peculiar structure 

 of the true Cotylosauria, but, inasmuch as the postsacral verte- 

 brae of Seymouria are of the ordinary slender type, the character, 

 though a useful one, cannot be profound. 



I believe that the cited genera at least are real reptiles — there 

 is no known reason for including them among the Amphibia — 

 but, until more is known about them than at present, a definite 

 position in the system can not be given them. One may con- 

 tinue to call them, following Baur and Thevenin, true Microsauria 

 as distinguished from the Lepospondyli; or he may, after Broili 



