286 CAPT. D. M. S. WATSON ON SEYMOURIA, 



least any that are tolerably well known. In the skull the 

 presence of the deep otic notch, the arrangement and number of 

 the temporal bones, the slender, elongate teeth, longest in the 

 maxilla?, and the shape, all differentiate the genus widely from 

 either Diadectes or Limnoscelis, as well as the chief forms now 

 referred to the Pariotichidse, and also from the known foreign 

 forms." "In "any event, it is certainly very remarkable that 

 this cotylosaur reptile with all its other strange amphibian 

 affinities should mimic so closely the temporal structure of the 

 real amphibians." " However, it is very much of a question 

 whether these resemblances [to Amphibia in skull and limbs] 

 are so much the result of heredity and relationships as of 

 adaptive, parallel, or convergent evolution. We have been 

 speculating on the assumption that the known temnospondylous 

 amphibians like Cacops, Eryops, Euchirosaurus, are, if not the 

 actual ancestors of the reptiles, their first or second cousins. 

 But this presumption is, in my opinion, quite unjustified." 



In several papers during the last five years, I have upheld the 

 view that Seymouria is the most primitive of all known reptiles, 

 and that its resemblances to Temnospondyls, particularly to the 

 Embolomeri, are due to inheritance. I now propose in the light 

 of a practically complete knowledge of the skeleton in the 

 Ootylosaurians Diadectes, Labidosaurus, Captorhinus, Limnoscelis, 

 Pariasaurus, and Procolophon, and in the Temnospondylous 

 Amphibia Eryops, Cacops, Tremaiops, Trimerorachis, Archeyo- 

 saurus, Lydekkerina, and Rhinesuchus, and a, good knowledge of 

 the skull and much of the skeleton in many Embolomeri, to 

 discuss tl\e position of Seymouria in detail. 



Labidosaurus and Captorhinus belong to the same family ; 

 each of the other forms represents an independent family ; Dia- 

 dectes, Paraisaurus, and Procolophon represent the superfamily 

 Diadectomorpha. The other Cotylosaurs are Captorhinomorphs 

 (Watson, 1917). 



The skull and lower jaw of Seymouria as a whole resemble those 

 of Labyrinthodonts in their reticulate ornamentation. Similar 

 sculpture is retained by the Captorhinomorpha alone amungst 

 Cotylosaurs, that of other types being less markedly composed of 

 pits, sometimes elongated to form long twisted channels. 



Basis Cranii. — The basioccipital of Seymouria agrees with those 

 of all other Lower Permian Cotylosaurs, rachitomous Amphibia, 

 and certain Embolomeri, in being excluded from the brain-cavity 

 by the meeting above it of special flanges from the exoccipitals. 

 Certain Embolomeri (Pteroplax) have the basioccipital entering 

 into the border of the foramen magnum, a condition which 

 appears to be the primitive one for Tetrapods. Seymouria is 

 unique amongst Cotylosaurs in the very large part which the 

 exoccipitals play in the cond}de. They form well-marked, down- 

 wardly-projecting areas strongly reminiscent of those of Eryops, 

 and not exactly paralleled in any other reptile. 



