386 



the face : they exhibit all entire subcaudal shields (at least on the 

 anterior part of the tail). 



VI. Neotropical or South American Region (Regio Neotropica). 



Characteristic forms. — \Epicrates, Xiphosoma, fCorallus, -fBoa, 

 Eunectes, * Chilabothrius, *Ungalia, Tortrix, Streptophorus, Homa- 

 locr anion, Elapomorphus, Elapocephalus, *Arrhyton, Liophis, Ste- 

 norhina, Erythrolamprus y * Hypsirhynchus, Xenodon (with smooth 

 scales), JJranops, Hydrops, Hyyina, *Gerarda, *IIipistes, Fieimia, 

 ■fDromicus, Psammophisl lineatus,Thamnodynastes, Dipsasl cenchoa, 

 Rhiiwbothryum, Leptognathus, Tropidodipsas, Scytale, Oxyrhopns, 

 *Elaps (with fifteen rows of scales), -fCraspedocejihalus, Lachesis. 



Forms common with other regions. — Rhinostoma, Rhabdosoma, 

 Tachymenis, Tomodon, Heterodon, Spilotes, Coryphodon, fllerpeto- 

 dryas, fP/iilodryas, fAhcetulla, ^Dryophis, Leptodeira, Eudipsus, 

 Dij)sadomo)phus, Dipsadoboa. 



If the number of species duly attributable to this region be rec- 

 koned at about 150, and its geographical area at 5,500,000 square 

 miles, we have a single species to every 36,000 square miles, or 

 nearly 2\ species to the same area, for which we found in the northern 

 region a single one. As for intensity of species, this region is far 

 surpassed by the East Indies, exhibiting only half as many species 

 for the same area, and therefore showing itself proportionally far less 

 productive of snakes than of birds. This fact will be very near the 

 truth, as we know nearly equal parts of both regions. In the ratio 

 of the different sections of snakes, South America does not agree with 

 any other region, showing a ratio between Boina and Colub?'ina= 1 : 8, 

 and between Viperina and Colubrina=l : 15. All the Boina have 

 only a single row of subcaudal plates, whilst the other tropical re- 

 gions exhibit such species with entire subcaudals as well as with two- 

 rowed. Among the Colubrine Snakes, it is rich especially in those 

 intermediate forms without prominent characters, the systematical 

 arrangement of which is far from being complete. 



Another character of the Region is, that true Lycodontidce are 

 wanting : they are replaced by Scytale and Oxyrhopus, in many re- 

 spects similar to the East Indian Lycodontidce, and forming a con- 

 necting link between these and the Dipsadidce. All the venomous 

 Colubrina belong to the genus Ehq)s, different from the East Indian 

 species by having fifteen rows of scales and another system of colora- 

 tion ; one or two species range into the southern parts of the former 

 region. Finally, all the Viperina exhibit a pit on the side of the face, 

 two-rowed subcaudal plates, and the head covered with scales, thus 

 being more closely allied to the greater part of the East Indian genera 

 than even to those forms which we meet with in North America. 

 One Viperine Snake with a rattle, Crotalus horridus, ranges into 

 this region ; but being also found in the more northern parts, and 

 having the other relations in North America, it must he reckoned 

 among those of the latter region. 



