500 Expedition to the 



frequent the villages of the prairie dogs, and to which they 

 have attributed the unnatural habit of voluntary domicilia- 

 tion with that interesting animal. It is true that the terge- 

 minus, 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 proof that it is 

 an acceptable inmate of the dwelling of the Arctomys. 



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 a distinct species. Specimens are in the Philadel- 

 phia museum. 



On the 5th July we left our camp at an early hour, and 

 ascended the Platte about ten miles. Here the party en- 

 camped for the day, and Dr. fames and Mr. Peale with 

 two riflemen, Verplank and Bernard, went out for an excur- 

 sion on foot, intending to ascend the Cannon-ball creek to 

 the mountains which appeared to be about five miles distant. 

 This creek is rapid and clear, flowing over a bed paved 

 with rounded masses of granite and gneiss. It is from a 

 supposed resemblance of these masses to cannon balls that 

 the creek has received its name from the French hunters. 

 The channel is sunk from fifty to one hundred feet below 

 the common level of the plain. 



This plain consists of a bed of coarse pebbles, gravel, and 

 sand, and its surface is thinly covered with prickly pears 

 and a scanty growth of starved and rigid grasses. Among 

 these, the hygrometric stipas, [S.juncea, S. barbata] are ex- 

 tremely troublesome, their barbed and pointed seeds adhering 

 and penetrating like the quills of the porcupine into every 

 part of the dress with which they come in contact. The 

 long and rigid awn is contorted or strait in proportion to 

 the humidity or dryness of the atmosphere, indicating the 

 changes in this respect with the precision of the nicest hy- 

 grometer. 



