134 JR. E. Call — Geographic and Hypsometrw 



Campeloma decision is a very abundant shell in Central 

 New York, in the Mohawk river and especially in the Erie 

 Canal wherein are to be found the optimum conditions for 

 development and growth. Indeed, as one passes from Maine 

 westwards to New York the form appears to become increas- 

 ingly abundant. It finds its maximum in individuals in New 

 York and either ceases entirely in the regions about or gradu- 

 ally is replaced by the other forms mentioned herein. 



Conrad's form, the geniculate variety, has been discovered 

 in South Carolina and onwards to middle Alabama. It is a 

 very common, often abundant shell in the larger streams of 

 Georgia and in the smaller ones of the northern portions of 

 that State and Alabama. Extensive collecting over all the 

 regions in northwest Georgia never failed to reveal it in all 

 streams in which mollusks of any sort were found, except, 

 indeed, in the very smallest. In most of the tributaries of 

 the Coosa it appeared and always with its well marked charac- 

 ters. Its range may be regarded as pretty well limited by a 

 line drawn along the Appalachians from the boundary of 

 North Carolina to near Wetumpka, Alabama, thence south- 

 eastwards to the Flint river at and below Albany. Thence it 

 passes northwards to middle South Carolina and to the place 

 of starting. Without this area it has not yet been detected. 

 What relation, if any, this peculiar form may sustain to the 

 conditions of its environment as a causal factor in determin- 

 ing its modification one may only guess rather than state. But 

 it is believed that therein will lie the explanation. 



The most widely distributed western species of Campeloma 

 is the form described by Anthony as C. subsolidum.. Under 

 the various synonymic names of C. milesii Lea and C. exilis 

 Anthony the typical shell occurs over a very extensive region, 

 embracing Indiana, Illinois, Iowa, Michigan, Minnesota, Ne- 

 braska, Kansas, Missouri, and portions of Arkansas and possi- 

 bly Kentucky. Specimens which are best referred to this 

 species have been submitted from Arkansas but they pass into 

 the more southern and characteristic Campeloma coarctation 

 Lea. Over southwestern Michigan and in Minnesota this shell 

 is very abundant and quite characteristic. In the lakes of 

 Northern Indiana and Illinois, as well as in those of Minne- 

 sota, the shells are lighter both in texture and in color than 

 when found in rivers or creeks. To this circumstance is due 

 the reference of very many specimens of this form, which is 

 quite characteristic, to Campeloma decisum. Throughout the 

 Upper Mississippi river this is the only species of Campeloma. 

 North of St. Louis it gradually grows more common becom- 

 ing abundant in that stream along Iowa and Illinois shores. 

 The most northern localities are Ft. Snelling, Minnesota, 



