CROTALUS, or RATTLE-SNAKE, in zoology, a genus belonging to the order of amphibia serpentes, the characters of which are these: The belly is furnished with scuta, and the tail has both scuta and scales; but the principal characteristic of this genus, is the rattle at the end of the tail. The rattles consist of several articulated crustaceous, or rather horny bags, which make a considerable rattling noise when the creature moves, and serves to warn people of their approach. There are five species, and the bite of every one of them is so highly poisonous, that it generally kills in a short time. 1. The horridus, or American rattle-snake, has 167 scuta, and 23 scutellæ. It is generally of an orange, tawny, or blackish colour on the back, and the belly is ash-coloured: they are from four to six inches in length; some are as thick as a man's leg: Dr Tyson dissected one which was four feet five inches long, and the body six and a half inches in diameter. They devour birds, squirrels, hares, &c. 2. The miliaris has 13 scuta, and 31 scutellæ. It is ash-coloured, interspersed with black spots, and is a native of Carolina. 3. The dryinas has 165 scuta, and 30 scutellæ. It is whitish, with a few yellow spots, and is a native of America. 4. The durissus has 172 scuta, and 21 scutellæ. It is variegated with white and yellow colours, and is likewise found in America. 5. The mutus has 217 scuta, and 34 scutellæ. It has a chain of rhomboidal black spots on the back, a black line behind the eyes, and is a native of Surinam.