842 The American. Naturalist. [October; 
are placed close together, as for instance Tretanorhinus and 
Helicops" and their associates. This is, however, a necessity 
of an artificial key and is not new in zoólogy. The charac- 
ters presented by the hemipenis are more readily determinable, 
and are more constant that those to be found in any other 
part of the structure. 
In furthez illustration of the same subject I present a 
synopsis of another tropical group, this time entirely Amer- 
ican, which only differs from the Xenodontine in the grooving 
ofthe posterior maxillary tooth, i. e., the Scytalinz. 
. I. Apex without calyces or spines, but with a membranous 
disc. (Disciferi). 
Hemipenis divided ; Erythrolamprus Boie. 
IL Hemipenis transversely or obliquely plicate ; (divided). 
(Flabellati). 
No calyces ; rostral plate normal ; Jaltris Cope. 
Calyces at apex ; rostral plate produced ; Conophis Peters. 
III. Calyeulate and not capitate. (Calyculati). 
e. Hemipenis divided. 
Rostral recurved ; Rhinostoma W agl. 
Rostral normal; pupil erect; Oxyrrhopus Wagl. 
Rostral normal; pupil round ; Philodryas Wagl. 
gg. Hemipenis undivided. _ 
Rostral normal ; Thamnodynastes Wagl. 
IV. Capitate (also calyculate). (Capitati). 
Hemipenis undivided; colubriform; ^ Coniophanes? Hallow. 
Hemipenis undivided ; fusiform ; Hydrocalamus Cope. 
V. Spinous to apex ; (divided). (Spinosi). 
Two nasal plates ; Tachymenis Wiegm. 
One nasal plate ; Tomodon D. & B. 
VI. Apex smooth, or with one row of spines; (divided). 
(Levi). 
Urosteges one rowed ; a band of minute advan: Scytale Wagl. 
Urosteges two rowed ; no calyces; Lygophis“ Tsch. 
1? Helicops is certainly to be placed in this family and has no relationship to the 
Natricine with which it has been hi therto rto associat ted. 
p 5 PY oe T y Py SUNG | E E with 
which I have proposed to unite it. j 
“Type Lygophis elegans Tsch.— Dryophylax poecilostornus Cope. 
