" ■'1 



THE HATRACHIA OF NORTH AMERICA. 



307 



This s[»ecic8 has the most iioitherii raujfc of those foiuul west of the 

 Mississippi, ami is especially cliaraeteristic of the elevated plains. It 

 nuijies from northern Texas to Montana. It resembles very closely 

 halfji'rown specimens of liuj'o coytiatmo^ the same region, sous tocon- 

 stituie it II mimetic analogue. 



Fui. 7S. ,s'y/i'(( haiiimiiiidii liouih!/iiii)s Oopp. OOW, iiat. size. Camp Tliorno, Yellowstone K. 



Meaaitremeiits of \o, :!5*i0. 



M. 



Li'iij;lli (if head ami body 0415 



Li'iiiftli of head, iiich.i'iiif; tympana 0V2 



\Vidtli of Ill-ad, iiicliidiiijj tyiiqiaiia OK! 



Li'ii;;tli of foit'-lt'ii from axill.i 0*^0 



L<'ii;;tli of Iiiiid Icj; from <;r(iiii 0445 



l.cii;;tli of tarsus 007 



[.(■njithof tibia 014 



l.fiiglli of rrstdf foot 017 



The specimen 9943, from the Yellowstone Kiver, is an excellent illus- 

 tration of the mode of origin of corneous ei)idermis. The end of the 

 muzzle and the frontal convexi*^y are covered with a layer of black 

 horn, each forming an oval shield, wliicli meets the other on the top of 

 the snout. This is probably a result of the constant jiressure anl fric- 

 tion of the earth when the animal is burrowing in it. Althoii„(i the 

 aninial burrows with the hinder limbs, the muzzle is naturally used in 

 keeping the passageway open to the surface. Tlie character is not con- 

 stant. 



This species is characteristic of the northern parts of the plains and 

 Great Basin. I found it especially common in tiie region north of the 

 Missouri Kiver and eastward of Fort Benton. Before my arrival there 

 rain had fallen, and the ruts of the wagon-trails were tilled with water. 

 These ditches contained numerous examples of this species, together 

 with Cliorophiliis Irisrriatus, Ilufo coiinatHs, and AmbUjHtoma tigrlmtm. 

 Their metainor|)hosis was completed by that time (August 20), although 

 some of the specimens were small. 



In Idaho, near latitude 4.5^ 30', is situated a body of water known as 

 Market Lake. Its extent is variable, for it is said to be dependent for 

 its water supi)ly on the overflows of the Snake Kiver, which is a few 

 miles distant to the eastward. An old channel leads from the river to 

 the lake, giving probability to the statement. , At the time of my pas- 

 sage through the region the water was unusually high, for a portion of 

 the stage road, with parts of numerous telegraph poles, was submerged. 

 The lake appeared to be about ten miles long by six in width. The 

 country surrounding it is arid, and the sand, which represents soil, rests 



m\ 



r 



