PRIMITIVE REPTILES . 651 



3'et ready to accept phylogenies and systems of classifications 

 based upon such vague distinctions. Neither am I convinced 

 that the quadrates of the Ichthyosauria and the Proganosauria 

 are of such a distinct type as to require the phylogenetic union 

 of the orders. 



Case has expressed the opinion that ''Mesosaurus is probably 

 an aquatic adaptation of the Cotylosaurian type" 12 and I have 

 also, independently, urged the relationships of the Proganosauria 

 with the Theromorpha under the assumption of a single temporal 

 vacuity. 13 Nevertheless, the Proganosauria, in their aquatic 

 adaptations are a definite group of primitive reptiles, of a distinct 

 type, as shown in their elongated maxillae, posterior nares, 

 elongated neck, long and flattened tails as figured by McGregor, 

 short, fan-like scapula, elongated propodials and shortened epi- 

 podials, et cetera. The vertebrae appear to be almost typically 

 cotylosaurian in their thickened arches and low spines. The ribs 

 are described as single-headed, attached below the diapophyses, 

 but I have given reasons for a different interpretation elsewhere. 



Aside from the distinctive aquatic adaptations, Mesosaurus 

 and Stereosternum show primitive cotylosaurian or theromoiph 

 characters in the presence of teeth on the vomers (prevomers) 

 deeply biconcave vertebrae, pectoral and pelvic girdles, entepi- 

 condylar foramen and ectepicondylar groove, carpus, tarsus, 

 digits, et cetera. The aquatic adaptations of the hmbs scarcely 

 differ more from the terrestrial theromorph structure than do those 

 of the dolichosaurs from the true lacertilians, and the aquatic 

 modifications of the skull are of but little greater moment than 

 those of the mosasaurs. 



However, I am wilUng to consider the Proganosauria as a 

 distinct order of reptiles until more shall be known about them. 



REPTILES OF THE LOWER PERMIAN OF EUROPE 



As an appendix to the foregoing discussion of the better known 

 lower Permian and upper carboniferous reptiles, the following 



1- Revision of the Cotylosauria, p. 118, 1911. 

 " American Permian vertebrates, p. Ill, 1911. 



