310 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii4 



Wisconsin: dane county: Lake Mendota in Madison, August 28, 1949, 

 A. A. Leath (PCH 262). juneau county: 17 miles southeast of Houston on 

 U.S. Ily. 16, July 22, 1958, Holt (PCH 796). 



Although these records give us but a general idea of the distribution, 

 several inferences on peripheral limits can be drawn. 



The distribution of the species in Kentucky appears to be essentially 

 as now laiown. The rather intensive traverse of the State made by 

 Dr. Holt in 1958 disclosed its presence in only two localities in the 

 lower part of the Green River drainage. Further east, in Barren, 

 Hart, and Edmondson counties, the species was apparently replaced 

 by an abundant member of the Philadelphica group. The apparent 

 absence of mesochorea from northern Indiana is more puzzling, there 

 being no reason why the species should not occur in the headwaters 

 of the Illinois River system. Yet the north-south traverse of western 

 Indiana made by Dr. Holt in July 1958, failed to reveal specimens 

 north of the latitude of Terre Haute. Clearly much more field work 

 needs to be done in the States of Illinois, Indiana, and Michigan. 



The records for western Massachusetts are almost certainly the 

 result of the introduction by man of the common midwestern crayfish 

 Orconectes immunis. Numerous collections from all parts of New 

 York State made by Denton W. Crocker contain no specimens of 

 mesochorea. 



Presumably this species has a very wide range of ecological toler- 

 ance. It has been collected from numerous species of crayfishes in 

 the genera Procamharus and Orconectes, in habitats ranging from 

 natural and artificial lakes through roadside swamps and ditches to 

 moderately cool gravelly streams. Whether C. mesochorea prefers a 

 particular microniche on its hosts is at present unkno^vn, but the 

 question could easily be settled by an investigator collecting almost 

 anywhere in the upper Mississippi Valley, where this species appears 

 to be perhaps the most abundant member of its genus. 



Remarks. — The general body outline, head shape, and other 

 characteristics give this species a strong superficial resemblance to 

 Cambarincola m.acrodonta Ellis. It is not surprising that, relying upon 

 jaw and body form for identification, Ellis should have misidentified a 

 Louisiana specimen as macrodonta, but it is remarkable that he could 

 have included such a conspicuously large-jawed creature as meso- 

 chorea among the paratype series of his own vitrea, which was diagnosed 

 in part by its small and homodont jaws. Doubtless a number of 

 existing literature records for macrodonta and 'philadelphica are 

 actually based upon the present species. I have, however, made no 

 attempt to piece together any information of this sort from published 

 works. 



