268 ZOOLOGY. 



Suh-order 2. Coluhrina. 



In the Coluhrina we miss the highly developed poison fangs which are 

 so conspicuous in the Viperina ; and the upper inaxilhiry bones, or edges of 

 the jaw, are well supplied with teeth. Some few of the species, however, 

 are poisonous, this being especially the case with the Hydridce, or water- 

 snakes, of the East Indies. Their venom fangs, however, are small, and 

 there are several teeth in a line behind the fangs. The head is of 

 moderate size, not conspicuously wider than the neck, and the crown in 

 one family is covered by a regular shield. Of the three families of the 

 sub-order, Hydrid(c, Boidcs, and Coluhridcc, the two first have the belly 

 covered with small, narrow, elongated scales, like those of the back ; while 

 in the Coluhridce the belly is covered with large, broad plates, each "one 

 extending entirely across the abdominal surface. 



Fam. Hydridce. This family, the species of which live almost alto- 

 gether in the water of seas, lakes, and rivers, are distinguished from the 

 Boidcs, with which they agree in the small scnles on the belly, by the 

 entire absence of spurs on each side of the anus, like rudimentary feet. 

 The ventral scales are narrow, hexagonal, or bandlike ; the eyes and 

 nostrils look upwards, the latter generally placed in the middle of a 

 shield with a slit or groove to its outer edge ; the fangs are of moderate 

 size, intermixed with the maxillary teeth ; the pupil is small and round, 

 and the tail is usually compressed into an oar, but sometimes conical. 

 Very many are poisonous. The species with compressed tails belong- 

 ing to Pelamis, Lapemis, Hydrus, &c., are true snakes, coiling them- 

 selves up on the shore, where they lay their eggs. Their food is said 

 to consist of seaweeds, although perhaps incorrectly. They are often 

 found asleep on the surface of the sen, and are then easily caught, as they 

 cannot descend without first throwing themselves on their backs, probably 

 to expel the air from their large vesicular lungs. They are often thrown 

 ashore by the surf, and are occasionally found in fresh water, having been 

 brought in by the tide, but they appear unable to live long out of salt 

 water. The fisheniien of the Eastern seas often catch them in their nets, 

 and hold them in great dread on account of the venom of their bite. The 

 species with conical tails appear to live principally in fresh waters. Some 

 recent authors have placed North American species under this family, 

 though apparently with much impropriety [Helicops abacurus, and erythro- 

 gramynus of Holbrook, with some others). PI. 90, fig. 7, represents Achro- 

 chordus jav nica, a species of this family from Java. 



Fa?7i. BoidiB. In this family, which contains species not poisonous, 

 indeed, but terrific on account of their gigantic size, wc find the ventral 

 scales or shields to be narrow, trrnsverse, and often six-sided. The hinder 

 limbs are developed under the skin, forn ed of several bones, and ending in 

 a short exserted spur, placed one on each side by the vent. The tail is 

 short, generally prehensile, and the pupil is oblong and erect, except in the 

 genus Tortrix. 

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