94 



BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



hutleri and the conditions with wliich it is found associated. It must 

 be acceded, in a general way, however, that, as far as our present 

 knowledge goes, its range is apparently included in the area lying 

 east of the prairie peninsula, which is characterized by the occurrence 

 of open forests on the uplands (fig. 30). If, as I hope to be able to 

 do, I can show that hutleri is genetically related to radix tliis dis- 

 tribution may be easily accounted for by the fact that as hutleri has 

 prairie afRnities, it might be expected to prefer conditions more in 

 accord with those of the treeless region. I have already shown 

 that the conditions in tliis region are somewhat intermediate between 

 those of the prairie and the denser forests of southeastern T'nited 

 States, and, if a direct relationship exists between hutleri and radix, 

 the coincidence between the range of hutleri and the open forest area 

 may be accounted for by the afRnities of both. This subject will be 

 reverted to in discussing its afRnities. It shoidd be noted, however. 



19-17 



17-19-17 



17-19-17-15 



3 



^^ 



50 



/a 



^fr 



-<^ 



2\ 



ii- 



Indiana. Michigan. Ohio. rcnnsylvania. 



Fig. 31.— DiAGR.VM SHOWING THE VARIATION IN THE DORSAL SCALE FORMULA IN THAMNOPHIS 



BUTLERI. 



that the range of hutleri is entirely within the glaciated area of eastern 

 North America which would indicate that the form is of post-Glacial 

 origin. 



Variation. — The characters of hutleri are quite constant and have 

 not by their variability given rise to much confusion. The scale 

 rows are invariably 19-17 in nearly all of the specimens examined, 

 but it should be observed (fig. 31) that while a larger formula has 

 never been observed, three of the Michigan specimens have the for- 

 mula 17-19-17 and both of the Pennsylvania (hrachy stoma) specimens 

 have 17-19-17-15, the smallest number observed. According to 

 Cope, the type of hutleri has 7 superior and 8 inferior labial plates, 

 a formula that holds for the Lake Makinkuckee, IVIiami River, and 

 Sandusky specimens (figs. 32 and 33). The Turkey Lake specimen 

 has the same number, except on the right side, where one superior is 

 dropped to leave 6. At Ann Arbor and Olivet, however, 6 supra- 



