1896.] DENTITION OF SNAKES. 615 
nation, to possess only half the real number. As early as 1856, 
the late Dr. J. G. Fischer (Verh. Naturw. Hamb. iii. p. 23) warned 
observers against such a fallacy. With a little experience, it is 
easy enough to ascertain whether teeth are accidentally missing or 
whether true diastemata are present. 
The author further mentions that the grooved teeth im the 
Opisthoglyphs vary in number from one to three. It should have 
been added that examples of as many as five grooved teeth occur in 
the genus Oxybelis. 
With regard to the Proteroglyphs, it is a matter for regret that 
Mr. West should not have had an opportunity of examining speci- 
mens with all the maxillary and some of the mandibular teeth 
grooved, such as we find in the genus Distira. The presence of 
grooves on the posterior “solid” teeth was first pointed out by 
Thomas Smith (Phil. Trans. cviii. 1818, p. 472), and later by J. G. 
Fischer (J.c. p.21). In 1890 (P. Z.S. p. 618) I recorded the 
presence of grooves on the mandibular teeth in a specimen of 
Distira, and I have since found them in-another genus of Hydro- 
phines, Aipyswrus (Cat. iii,p. 303) and in an Elapine, Glyphodon 
(t.c. p. 313). It would have been highly interesting to ascertain 
whether any connection exists between the poison-gland and the 
small grooved maxillary teeth, and whether any correlative modifi- 
cation of the sublabial glands obtains in those forms in which the 
mandibular teeth show grooves. 
I have previously expressed the opinion that the Viperine 
maxillary may be regarded as derived from the Opisthoglyph. In 
order to trace the probable evolution of the maxillary in Snakes, 
it suffices to survey the multitudinous modifications offered by the 
existing forms, for although possibly not one of them represents 
the actual groups through which evolution has taken place, they 
show clearly enough the various steps connecting the extreme 
types and the probable derivation of one type from the other. 
In the first place, the hypothetical primitive Ophidian dentition 
is exhibited by Xenopeltis (Cat. i. p. 168), in which the maxillary, 
premaxillary, and dentary are armed with very numerous, closely 
set, equal solid teeth. Next we have Polyodontops (t. c. p. 181), 
which only differs in the absence of teeth on the premaxillary 
bone. From this type numerous and gradual modifications arise 
through reduction in the number of teeth and irregularity in their 
size, leading to Boodon (t.c. p. 327) among the forms with persis- 
tent hypapophyses throughout the vertebral column, in which some 
of the anterior teeth, situated near the palatine process of the 
maxillary, become enlarged and fang-like, although still devoid of 
grooves. From such a type we may reasonably assume the Elapines, 
which still retain the hypapophyses, to have been derived through 
abbreviation and suppression of the portion of the maxillary 
anterior to the palatine process concurrently with the develop- 
ment of grooves in the anterior fangs. In the series now reached, 
the Elapine (Cat. iii. p. 310), the groove becomes deeper and 
deeper, the margins of the tooth ultimately coalescing to form the 
