SAND-SNAKES. 193 



Could we but see the boa during the night in the depths of its native forests 

 ■ — at which time alone it is thoroughly active — we should doubtless obtain a very 

 different idea of the creature than that which we gather from the inspection in the 

 daytime of the lethargic specimens in menageries. Lying coiled on the branch of 

 some large tree, with its head projecting ready to be darted on its prey with the 

 rapidity of lightning, the boa is generally unobserved by the passing traveller 

 unless it happens to make a dart at an unfortunate dog belonging to his party. 

 Feeding generally on such mammals as agutis, pacas, rats, and mice, which are 

 destroyed in the manner from whence is derived its trivial name, the boa, when it 

 attains unusually large dimensions, is also capable of killing deer and large dogs ; 

 while it is always ready for such birds as it can capture, and does not disdain, 

 when in captivity, a meal of eggs. The stories of its killing adult human beings 

 and horses are, however, mere fabrications. Nothing is known of the breeding- 

 habits of this snake and its kindred in a wild state ; but from observations made 

 on specimens in captivity, it appears that the eggs are generally hatched within 

 the body of the parent, although one instance is on record where young and eggs 

 were produced simultaneously. To European palates, snakes would probably be 

 highly unacceptable as food, however temptingly they might be dressed ; but in 

 Eastern South America, the flesh of the boa is regarded as a most dainty dish, 

 while its fat is reputed to be highly efficacious in the healing of various diseases. 

 The skin is used to ornament saddles and bridles, and for other decorative purposes. 

 None of the other members of the genus attain dimensions equal to those of the 

 common boa, the Malagasy species being the smallest of all. 



Keel-Scaled The last representative of the section of the subfamily in which 



Boa - the head is well defined from the neck, and the tail more or less 



prehensile, is the keel-scaled boa (Casarea dussumieri), of Bound Island, near 



Mauritius, distinguished as a genus by the keeling of the scales, and the long tail ; 



its other general characters being similar to those of the true boas, except that the 



nasal shields of the head are separated by a pair of internasals. This snake, which 



attains a length of about 4 feet, and has a prominent and obliquely truncated 



muzzle, is either uniform pale brown above, or brown with two dark stripes and a 



lateral series of small spots down the body, a dark streak on each side of the head 



through the eye, and the under-parts either plain yellow or yellow spotted with 



black, the under side of the tail always having such spots. 



The snakes of this genus, together with those of three allied 

 Sand-Snakes. . , . 



genera, which are the remaining members of the family, may be 



distinguished at a glance from the boas and their allies by the gradual passage of 



the head into the body without any constriction at the neck ; while they are 



further characterised by the tail being, at most, only slightly prehensile. From 



their allies, the sand-snakes are distinguished by the small scales being either 



smooth or singly keeled, and by the head being covered with small shields, of 



which the rostral is enlarged. The eye is small, and sometimes minute, with a 



vertical pupil ; while the body is cylindrical ; and the very short tail, which is 



frequently without any power of prehension, has a single row of shields on its 



lower surface. These snakes are represented by seven species, with a geographical 



distribution including Northern and Eastern Africa, and Southern and Central 



vol. v. — 1$ 



