Rattle-snakes of a particular species[133] are sometimes seen in these villages. They are found between the Mississippi and the Rocky Mountains, and appear to prefer an unproductive soil, where their sluggish gait may not be retarded by the opposing obstacles of grass and weeds. Whilst exploring Bowyer creek of the Missouri, in the spring of 1820, our party met with six or eight of them during one day's march on the prairie; and on our subsequent journey to the Rocky Mountains, we several times encountered equal, or even greater numbers, in the same space of time. This is the species of serpent which travellers have observed to frequent the villages of the prairie dogs, and to which they have attributed the unnatural habit of voluntary domiciliation with that interesting animal. It is true that the tergeminus, like many other serpents, will secure a refuge from danger in any hole of the earth, rock, or fallen tree that may present itself, regardless of the rightful occupant; but we witnessed no facts which could be received as a proof that it was an acceptable inmate of the dwelling of the arctomys. [133] _Crotalus tergeminus_, S.—_Body_ dusky cinereous, a triple series of deep brown spots; beneath with a double series of black spots. _Body_ pale cinereous brown, a triple series of fuscous spots, dorsal series consisting of about forty-two large, transversely oblong-oval spots, each widely emarginate before, and obsoletely edged with whitish lateral series, spots transversely oval, opposite to those of back; between the dorsal and lateral series is a series of obsolete, fuliginous spots, alternating those of the two other series; _head_ above with nine plates on the anterior part, on which are a band and about three spots, two undulated vittæ terminating and confluent with the first spot of the neck, a black vittæ passes through the eye, and terminates on the neck each side; _beneath_ white, a double irregular series of black spots, more confused towards the tail; _tail_ above, with five or six fuscous fasciæ, beneath white irrorate with black points, six terminal plates bifid. Length 2 ft. 2⅛ in. tail 2⅛ in. Plates of body 151 of tail 19 Bifid plates at tip 6 Another specimen, much smaller, Pl. 152. subcaudal, 20. scales at tip 3.—JAMES. {184} From the disparity in the number of plates and scales, and from the greater size of the vertebral spots in this species than in the C. miliaris, we have been induced to consider this as a distinct species. Specimens are in the Philadelphia museum.