THE n.\TRACIIIA OF NORTH AMERICA. 



395 



rope eastwards to tlie Sierra Nevada or to the Rocky Mountains. In 

 this j-enns is repeated the plienonienon observable elsewhere, that 

 the species of the Atlanti*! Coast region are more ditlerent from tbose 

 of the Old World than are those of the Pacific coast. 



The longitudina' dorsal iid;,'esc(Mistitulea peculiar featun' not found 

 in any of the other j;enera of Ilatraithia Salientia of the United States. 

 They exist ill most of the species, with tiie exception of It. catcsblana 

 and l\. monte:ii)uac. Sometimes the skin above is perfectly smooth, 

 sometimes roughened by tubercles; the same species will occasionally 

 present both extremes under different cir<!umstan(;es. Tlu; vocal sacs — 

 one on each side of the throat — are, when inflated, visible externally 

 in /»'. rirescens, areohita, and moiitczuiiKi' ; i)ossibly in others. Tiie 

 amount of web!)ing between the toes varies from the fullest condition 

 in />'. cdtcshiaita, scptcntrionaUn, and boijlii, to the half webbing of li. 

 arcolala. 



The distinctive characters of the sjjecies are derived from the com 

 ])arative bidk of the body or limbs ; the presence or absence of dorsal 

 ridges ; the comparative length of fore arm and hand ; of femur, tibia, 

 foot, and body; the amount of weltbiiig between the toes; the compara- 

 tive length of the third and fifth toes (the fourth being always longest); 

 the shape of the tongue; the position of the vomerine teeth ; the size of 

 eye and tympanum, etc. The colors ma.\ present dark blot(;hes, areo- 

 lated or not, reticulations or marmoratioiis on a light ground, or light 

 sinuations or sj»ots on a dark ground. Many species Iiave a light line 

 along the .jaw, which begins distinctly either at the nostrils or under 

 theeye. Those in which this line is wanting are E.cafenbiand^monfezunKC, 

 areolatii, scpfenfrionalis, Idi/JH, and some vaiieties of clainata. Speci 

 mens vary much, even of t he saiiu' species, with latitude and external cir- 

 cumstances. As a general lule, those from the north are larger, darker, 

 ami more pustular, so much so, that for li. cideshiaiut, patustris. cin'scens, 

 and chnnafa it is <piite easy to establish two or three different races, 

 some of them even raised to the rank of distinct s[)ecies. As, however, 

 all intermediate stages may be detected on a close examination ot many 

 specimens from the same locality, alrliuugh a general adherence to the 

 tyiK- is preserved, it becomes imi>ossible to assent to the retention of 

 several long-established species. 



The following tabular analysis gives in a synoptical form the most 

 salient features of the different species. It is, however, impossible here, 

 as elsewhere, to indicate characters which shall apply with mathemat- 

 ical accuracy to all s))eciinens of the same species. The dimensions, 

 pro|)ortions, color, and other characters may vary to a considerable ex- 

 tent, and it is only by striking the balance of all the features of a spe- 

 cies that we cau detcrmiuo its true position. 





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