Boulenger's phylogenetic system stands as follows: Viperidae Uropeltidae C. Opisthoglypha C. Proteroglypha Amblycephalidae mandible to the aglyphous or innocuous Colubridae, whence further differentiation in three new lines has taken place, - (i) the harmless Amblycephalidae as a side-issue, (2) the very poisonous proteroglyphous Elapidae, (3) the moderately or incipiently poisonous Opisthoglypha, out of some of which seem to have arisen the venomous Viperidae.
He adhered to this arrangement in his last comprehensive work (Crocodilians, Lizards and Snakes of North America, 1898, Smithsonian Inst., 1900), but combined the Asinea and Proteroglypha as Colubroidea, subdividing these into Peropoda, Aglyphodonta, Glyphodonta, Proteroglypha and Platycerca (Hydrophinae).
Mus., 1893-1896) accepted Cope's principles, and mainly by .combining the Asinea of Stannius and Cope with the Proteroglypha as Colubridae - wherein he was followed by Cope, as mentioned above - and separating therefrom the Peropoda or Boidae, he has produced a logically-conceived system, by far the best hitherto proposed.
Cope (Proc. Ac. Philad., 1864, p. 230) resorted to the modifications of the squamosal, ectoand endopterygoid bones, the condition of the vestigial limbs, and the teeth:- Scolecophidia (Typhlopidae), Catodonta (Glauconiidae), Tortricina (Ilysiidae and' Uropeltidae), Asinea, Proteroglypha and Solenoglypha.
Nat., Paris, 1851,1851, p. 199) distinguished between Opoterodonta, Aglyphodonta, Proteroglypha and Solenoglypha.