148 S. W. WILLISTON 



cially such forms as Seymouria Broili' are about as close to the temno- 

 spondylous amphibians, save in the palatal structure, as it would be 

 possible to have them and still call them reptiles; unless, indeed, 

 we accept Boulenger's rather improbable views and derive the 

 double-arched forms from the Microsauria and the stegocrotaphous 

 and single arched from the Temnospondyli. And here too, the 

 Chelonia upset our best-laid schemes. Not all dinosaurs possess 

 such ribs, and I do not think that their loss, without other important 

 differences is of great moment. And by no means is it yet sure that 

 the Cotylosauria, and the acleithral forms were without them. Indeed 

 I believe that we shall find some of them with such ribs eventually. 



Our " Labidosaurus incisivus^^ differs from Telerpeton chiefly 

 in the sculptured skull, a character which that genus shares with 

 Procolophon and Sclerosaurus,^ and from Procolophon in that and 

 the character of the teeth, and in practically nothing else. If 

 Procolophon be admitted to a distinct order, superorder, and subclass 

 from Telerpeton, what shall we do with Telerpeton, Pariotichus, 

 Labidosaurus, Elginia, Sclerosaurus, etc. ? They all lack the cleith- 

 rum; they are, for the most part at least, small, crawling reptiles 

 and can hardly be united with Pareiasaurus nor with Diadectes and 

 Otocoelus. Shall we erect a new order for them? 



The resemblances between the pectoral and pelvic girdles of 

 Dimetrodon and our present specimen are evident at a glance. But, 

 the Pelycosauria, notwithstanding the two temporal vacuities of the 

 skull, and its supposed membership in the Diaptosauria, have well 

 developed cleithra, and that character must be added to the Diapto- 

 sauria as well as to the Cotylosauria and Pareiasauria ! 



I may add, by way of postscript, that, in a recent review of the 

 literature of the reptilia, I find all of the older groups usually called 

 orders have been raised in recent years by well-known writers to super- 

 ordinal or subclass rank, save the Ichthyosauria and Chelonia, the 

 two groups of all others most entitled to high rank! And most of 

 the suborders have been elevated to orders — thirty or more. And 

 what has been gained ? 



1 Paleontographica, 1904. 



2 Von Huene, Geologische pal. Abhandlungen, X, 1902, p. 29. 



