286 CAPT. D. M. S. WATSOK^ ON SKYMOURIA, 



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

 presence of the deep otic notch, the ai-i-angement and number of 

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

 niaxillaj, and the shape, all differentiate the genus widely from 

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

 referred to the Pariotichidpe, and also from the known foreign 

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

 this cotylosaur reptile with all its other strange a.mphibian 

 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 Caco'ps, 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 ps-actically complete knowledge of the skeleton in the 

 Ootylosaurians Diadectes, Lahidosaurus, Captorhinus, Limnoscelis, 

 Pariasmtrus, and Procolophon, and in the Temnospondylous 

 Amphibia Eryops, Gacops, Tretnatops, T rimer or achis, Archego- 

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

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

 discuss the position of Seymouria in detail. 



Lahidosaurus and Captorh'mus belong to the same family ; 

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

 dectes, Paraisaicrics, and Procolojyhon represent the superfamily 

 Diadectomorpha. The other Cotylosaurs are Captorhinomorphs 

 (Watson, 1917). 



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

 of Labyi-inthodonts in their reticulate ornamentation. Similar 

 sculpture is retained by the Captorhinomorpha alone amongst 

 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, lachitomous Amphibia, 

 and certain Embolomeri, in being excluded froin 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 condjde. They form well-marked, down- 

 wardly-projecting areas strongly reminiscent of those of Eryops, 

 and not exactly paralleled in' any othei- reptile. 



