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Show 1896.] DENTITION OP 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 in 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 specimens with all the maxillary and some of the mandibular teeth grooved, such as we find in the genus Bistira. The presence of grooves on the posterior " solid" teeth was first pointed out by Thomas Smith (Phil. Trans, cviii. 1818, p. 472), aud 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 Bistira, and I have since found them in another genus of Hydro-phines, Aipysurus (Cat. iii. p. 303) and in au 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 modification 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, prsemaxillary, and dentary are armed with very numerous, closely set, equal solid teeth. Next we have Polyodontophis (t. c. p. 181), which only differs in the absence of teeth on the prseinaxillary 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 persistent 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 development of grooves in the anterior fangs. In the series now reached, the Elapinae (Cat. iii. p. 310), the groove becomes deeper and deeper, the margins of the tooth ultimately coalescing to form the |