OCR Text |
Show APPENDIX C.- REPTILES. 387 from S. maculatm, the chief character of which consists in the truncated snout. The eyes are of medium size, situated behind the angle of the mouth. Their position and size in S. maculatus we do not know accurately, but in S. mextcanus these organs would be considerably smaller and more approximated to the end of the snout, judging of these peculiarities from the various sketches given of that species, and proportionally much smaller than in a specimen of Siredon in our possession from the city of Mexico, and of about the same size as our S. lichenoides. If these proportions are correct in the drawings of S. mexicamis, we would undoubtedly have a species which could not be accurately characterized until further information should be obtained. The nostrils are very small and near the end of the snout. The body is sub-cylindrical, subfusiform, broader and deeper at its origin than on any point backward. The tail is very much compressed, elongated, and tapering into a point. The dorsal membrane commences at the occiput, rising gradually until the middle of the tail, whence it diminishes again toward its pointed tip. The membrane under the tail is lower than that above, extending from behind the vent to the tip of the tail, and reaching its greatest height on its anterior third, but? diminishing more rapidly forward than backward. The anal opening is very large, elongated, and rendered very conspicuous by the great development of the fleshy masses which constitute its margin. The presence of four external flaps, provided with respiratory fringes, is a generic character, belonging to all the species hitherto known. Their real appearance has been misrepresented in many sketches, as we could satisfy ourselves by the examination of two species preserved in alcohol. The branchial fringes do not extend all along the upper edge of the branchial flap. They occupy densely the lower edge of that cutaneous appendage from its origin to its tip, and thence for a short space above, but much less developed here than below, as we have endeavoured to show in the profile of fig. 2. The fringes themselves are very much flattened, tapering, and disposed upon a double row, so that each of them appears as if double; but it is easy to ascertain that the row on either side does not combine with the other. The fore and hind legs have nearly the same length when measured from their bases to their extremities; the hind ones, however, are much thicker, and the toes of both pairs are neither so slender nor so elongated as in &. mexicanus and S. maculatus. The ground colour is blackish brown; there are irregular patches 22 |