1886.] 481 [Cope- 



sufficient. For the definition of the genera distinct characters exist, 

 although the suhject is one of much difficulty. The object of definition 

 being, as I imagine, precision, and the consequent increased facility of de- 

 termination, I have employed all structural characters whatever, and only 

 neglected them where it is evident that they are inconstant within the limits 

 of a species. I find of the greatest importance the grooved or non grooved 

 characters of the posterior teeth, and the absence or number of the scale- 

 pits. The division or non-division of the anal scutum is also of much im- 

 portance, although in a very few genera (e. g., Xenodon) it is not con- 

 stant. Relying, as the system always must, on exact characters, I have 

 not allowed considerations of "physiognomy " to change a result where it 

 conflicts with structure, which is, however, rarely the case. The tendency 

 of some authors to neglect characters and to depend on "physiognomy" 

 destroys precision and explains nothing, besides rendering identification of 

 species most laborious, resting as it must in that case on purely empirical 

 methods. I also do not use as generic characters the number of rows of 

 scales, or of labial scuta, believing that these are only available in the dis- 

 tinction of species. 



In a few instances I have not been able to examine the skeletons of gen- 

 era of doubtful position, so that their reference to a family division may - 

 yet have to be altered. I have, however, studied the fine series in the 

 museums of Paris and Washington, besides a considerable number in my 

 own collection. For the characters of many genera which I have not seen 

 I have had to rely on the descriptions of others, especially of Drs. Peters 

 and Giinther. 



EPANODONTA. 



TYPHLOPIDxE. 



I. Muzzle covered above by rostral and internasal scuta. 



«. Two ocular plates and a preocular. 

 One nasal plate Letheobia Cope. 



aa. One ocular and a preocular. 



One nasal plate • Typhlops Schn. 



Two nasal plates Helminthopliis* Pet. 



aaa. One ocular and no preocular. 



One nasal plate Tt,phlina\ Wagl. 



Two nasal plates Liotyphlops% Pet. 



II. Muzzle and front with five symmetrical scuta. 



Two nasals and a preocular A?iomalepis Jan. 



CATODONTA. 



STENOSTOMID^E. 



Superciliary scales present Stenostoma Wagl. 



No superciliary scales Rma B. & G.§ 



* Idiot yph lops Jan. 



+ Pilidion Dum, Bibr. Typhlinalis Gray. 



% Rhinotyplops Pet. 



QCatodon D. & B., not of Lacep. Siugonodon Peters. 



