48 BULLETIN 32, UNITED STATES NATIONAL MUSEUM. 



No iKistorbital or supraorbital bones; premaxillary teeth i^vesout . . Xenopeltidw Cope. 

 (33. No coronoid bone. 

 /?. Postorbital bone produced over the superciliary region. 



No gastrosteges Acrochordidce Cope. 



Gastrosteges present Nothopidw Cope. 



/:?/?. Postorbital bone not extending over the superciliary region. 



d. Nostril in or between nasal plates Coluhridw Auct. 



£. Vertebral hypapophyses confined to the anterior part of the column, 



Hatrieinw, 

 ££. Vertebral hypapophyses extending throughout the column, 



Colubrince Cope. 

 88. Nostril in the rostral plate Jcontiophidw Gthr. 



V. Os maxillare horizontal, thickened in front, and not reaching the premaxil- 



lare anteriorly, and bearing a perforate tooth. Proteroglypha. 

 a. Caudal hypapophyses bifid ; caudal neural spines and pleurapophyses short. 



Postfrontal bones wanting ; fang grooved Elapidce Cope. 



Postfrontals present ; fang grooved Najidw Cope. 



Postfrontals present ; fang not grooved Dendraspididw Gthr. 



txa. Caudal hypapophyses simple ; caudal neural spines and pleurapophyses 

 elongate. 

 A postfrontal bone Hydrophidce Gthr. 



VI, Maxillary bono vertical, not reaching premaxillary, articulating with the pre- 



frontal by a ginglymus, and to the ectopterygoid without imbri- 

 cation, and bearing a perforated tooth Solenoglypha. 



Maxillary bone not excavated ; fang not grooved in front ; no postfrontal bone, 



Atractaspididw Gthr. 

 Maxillary bone not excavated ; fang grooved in front ; a postfrontal.. Cawsidfl? Cope. 



Maxillary bone not excavated ; fang not grooved ; a postfrontal Vtperidw Grey. 



Maxillary bone excavated by a large chamber ; fang not grooved in front ; a post- 

 frontal Crotnlida; Gray. 



In the following pages I present synoptical diagnoses of the genera of the Ophidia 

 arranged in key form. These are placed under subfamily heads which are not, with 

 the exception of the Homalopsina^, defined. It is not certain, therefore, that their 

 contents are in all cases properly limited or distributed. It remains a desideratum, 

 to discover the characters of the natural divisions of the Colubridse, if any there be. 

 The characters presented by Dum6ril and Bibron, and by Giinther, are important but 

 insufificient. For the definition of the genera distinct characters exist, although the 

 subject is one of much difficulty. The object of definition being, as I imagine, pre- 

 cision and the consequent increased facility of determination, 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 importance, although in a very few genera (e. g., Xenodon) it is not constant. 

 Relying, as the system always must, on exact characters, I have not allowed consid- 

 erations 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 ren- 

 dering 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, or the size of the eye, believing that these are only 

 available in the distinction of species. 



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

 doubtful position, so that their reference to a family division may yet have to be 

 altered. I have, however, studied tU§ fine series in the museiitns of Paris and, W*.8hj,n^- 



