104 



BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



There is thus no geographical variation shown conclusively in the 

 averages, but it should be noted that the longest tails are found in 

 Louisiana, which may indicate a tendency toward an increase in the 

 length of this organ in this region (lig. 38), w^hile the shortest tails 

 occur in Texas. 



Less evidence is at hand regarding the number of subcaudal scutes 

 than is the case in any other series of scales, largely owing to the fact 

 that the tail of many specimens is broken. The extremes are 

 75-125, an extent of variation which is equaled in no other form in 

 the genus. The averages are not to be relied upon, but it may be 

 seen from the table (fig. 39) that the smallest number occurs in the 

 southwestern part of the range and the largest number in Louisiana. 

 In this case, however, the variation in the number of subcaudal scutes 

 is apparently associated with a variation in the tail length and afl'ords 

 no evidence of the dwarfing shown bv the other characters. 



A 



.55 



.25 



5n 



24. 



IT 



la 





._ - --ir 



Mt. Carmcl, St. Louis, New Orleans, Tule Canon, Austin, Veracruz, 



Olney, Missouri. Perry, Pecos, San Brownsville, Yucatan. 



Illinois. Louisiana. AngeIo,Texas. Texas. 



Fig. 38.— Diagram showing the variation in the proportionate tail length in Thamnofhis 



sauritus proximus. 



There are few variations in coloration that deserve mention. Occa- 

 sionally the dorsal stripe is red, but how frequently we do not know", 

 since this color rapidly disappears in alcohol. Occasionally, also, 

 this stripe becomes somewhat obscure, but both of these characters 

 are apparently liable to crop out almost anywhere in the range. 

 The type of Eutsenia rutiloris Cope is characterized by this obscurity 

 of the dorsal stripe, although the latter is visible throughout the 

 entire length of the body. The only other character (and the prin- 

 cipal one) upon which this form was based was the presence of red 

 upon the "superior and inferior labial plates and the first three large 

 gastrosteges." This color is now faded and I have never observed 

 a specimen of proximus which exhibited it, but the specimen differs 

 in no other way from the Yucatan specimens of proximiis, and the 

 character is of too little importance to justify the separation of 

 this specimen from proximus (See Ruthven, 1906a). 



To summarize the variations in proximus: 



