840 The American Naturalist. - [October, 
In the fresh-water snakes (Natricine) there is no tracheal 
lung. The hemipenis of this group is very characteristic;. 
(Plate XXXVII fig. 8). 
As an illustration of the modifications in classification 
necessary in view of the characters which I have observed, I 
give an analysis of the genera of the group which I have 
called the Xenodontinze. These genera belong mainly to the 
southern Hemisphere, and chiefly to the Neotropical Realm, a 
few genera occcuring in Africa and North America. The 
characters of the division are as follows. 
Hemipenis with bifurcate sulcus spermaticus, and armed 
with well developed spines, which are developed from the 
marginal papille of calyculi, when the latter are present. 
Hypapophyses of the vertebre generally present only anter- 
iorly.° 
. A. Lung without large proximal diverticulum. 
I. Apex of hemipenis without calyces or spines but with a 
membranous disc. (Disciferi Fig. 7), 
e. Rostral plate not recurved. 
Hemipenis undivided, no scale-pits ; Aporophis Cope. 
Hemipenis divided ; no scale-pits ; Opheomorphus Cope. 
Hemipenis divided; one scale-pit ; Xenodon *Boie. 
vv. Rostral plate recurved. 
Hemipenis divided; one scale-pit ; Lystrophis Cope. 
II. Hemipenis transversely plicated (divided): (Flabellati). 
Plicæ not pappillose ; diacranterian ; Helicops Wagl. 
Plicee not pappillose ; isodont ; Pseudoeryx’ Fitz. 
Plicze pappillose ; isodont ; Rhabdosoma’ D. & B. 
III. Calyeulate, and not capitate (Calyculati). 
v. Hemipenis undivided. 
Fusiform ; isodont ; Carphophiops Gerv. 
Colnbriloria : madoni. two nasals; Diadophis B. & G. 
Colubriform ; diacranterian; one nasal; Amastridium Cope. 
* American Naturalist, 1893, p. 481. 
5In Helicops they are continued to the tail. 
5 Including Liophis Wagl. 
t Dimades Gray. 
8 Catostoma and Adelphicus are closely allied. 
