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 

 easj' enough to ascertain whether teeth are accidentally missing or 

 whether true diastemata are present. 



The author further mentions that the grooved teeth in the 

 Opistboglyphs vary in number from one to three. It should have 

 beeu added that examples of as many as five grooved teeth occur in 

 the genus Oxyhelis. 



With regard to the Proteroglyphs, it is a matter for regret that 

 Mr. West should not have bad an opportunity of examining speci- 

 mens with all the maxillary aiid some of the mandibular teeth 

 grooved, such as we find in the genus Dislira. The presence of 

 grooves on the posterior " solid " teeth was first pointed out by 

 Thomas Smith (Phil. Trans, cviii. 1818, p. 472), and later bv J. G. 

 Fischer {I. 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, Aipysurus (Cat. iii. p. 303) and in an Elapine, Olyplwdon 

 {t. e. 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 Vipejine 

 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, 

 praemaxillary, and dentary are armed with very numerous, closely 

 set, equal solid teeth. Next we have Pohjoclontophis (t. c. p. 181), 

 which only differs in the absence of teeth on the priemaxillary 

 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 ElapinsB (Cat. iii. p. 310), the groove becomes deeper and 

 deeper, the margins of the tooth ultimately coalescing to form the 



