2548 SCALED REPTILES 



first three genera may be distinguished by the tail being but very slightly, if at all 

 prehensile, and by the rostral shield of the head being either devoid of pits, or with 

 only very shallow ones. The first genus (Loxocemus}, as represented by a single 

 comparatively-small Mexican species (L. bicolor), has no pits in the labial shields, 

 no loreal shield, and the nostril situated in a single nasal shield. Nardoa boa, of 

 New Ireland, alone represents the second genus, and may be distinguished by the 

 presence of pits in the lower labial shields, and by the laterally placed nostril being 

 situated between two nasal shields. On the other hand, the third genus, Liasis, is 

 represented by several species ranging from Flores and Timor to Papua and the 

 north of Australia; and may be distinguished from the second by the nostril being 

 placed more superiorly in a half-divided nasal shield. Finally, three genera in 

 which the anterior jawbones, or premaxillae, are toothless are Chondropython, with 

 one Papuan species; Aspidites, represented by two species from the north of Aus- 

 tralia, and Calabaria, with a single West-African representative. The interest at- 

 taching to these snakes is the connection which they form between the pythons and 

 the boas. Thus while the first two differ from the typical pythons and resemble 

 the boas in the presence of teeth on the palate, the second and third likewise agree 

 with the latter in having the shields on the lower surface of the tail mostly or en- 

 tirely single; the tail itself being but slightly, if at all prehensile. 



The tree boas of tropical America may be taken as examples of the 

 second subfamily (Bointe) of the assemblage of snakes under consid- 

 eration. The members of this subfamily can be distinguished from the preceding 

 group solely by the absence of a supraorbital bone on the upper surface of the skull 

 above the socket of each eye. They further differ from all the pythons, with the 

 exception of two of the three genera last mentioned, in having teeth on the palate; 

 and, with the exception of the whole three of the connecting genera, in the absence 

 of teeth in the anterior upper jawbones, or premaxillae. Moreover, the boas and 

 their allies further differ from the typical pythons in having the shields on the lower 

 surface of the tail for the most part single, thereby agreeing with the genera As- 

 Pidites and Calabaria, and thus showing that the small group to which the two lat- 

 ter belong forms such a close connection between the pythons and boas as to preclude 

 their reference to separate families. 



In common with the majority of the thirteen genera, into which the subfamily 

 is divided, the tree boas are characterized by having the head distinctly defined from 

 the neck, and the tail more or less prehensile. They are specially distinguished by 

 the anterior teeth being much larger than the hinder ones; by the smooth scales of 

 the body; by the presence of shields on the head, and by the labial shields being 

 either devoid of pits or with only shallow ones. In form the body is more or less 

 compressed, and the tail either moderate or long; the eye is of medium size with a 

 vertical pupil, and the shields on the head may be either small and irregular, or 

 large and symmetrical. 



These snakes are represented by nine species, the largest of which is the pale 

 headed tree boa (Epicrates angulifer) of Cuba, attaining a length of about seven 

 feet; another well-known species being the streaked tree boa (E. striatus} from 

 San Domingo and the Bahamas. The thick-necked tree boa (E. cenchris), must, 



