OF CONCnOLOGY. 35 



Without assuming, however, to decide any question of differ- 

 ence or of identity between '•^ ponderosa " of the Coosa and of 

 the Ohio system of rivers, I shall take it for granted, in the 

 presence of much convincing evidence and in the absence of all 

 evidence to the contrary, that the true '■''Pal. coarctata, Lea," is 

 the young of a species found in the Coosa River, the adult of 

 which is known as ponderosa. If this is not a correct inference 

 no one will be more ready than myself to accept convincing 

 testimony in the premises. 



Having shown, as I think, in a satisfactory manner what may 

 be regarded as M. coarctata, I desire to call attention to other 

 suggestions derived from an examination of Mr. Wheatley's 

 specimens. In his collection are numerous specimens, typical 

 specimens as well as those of a more varied character, illustrat- 

 ing two of Mr. Anthony's species. These specimens, together 

 with others in my own' collection, suggest in the most positive 

 manner that M. exilis and M. suhsolida are extreme varieties 

 of one species. In geographical distribution they seem to range 

 through the sluggish side streams of the Mississippi Valley from 

 Iowa to Natchez. How much more extended their distribution 

 may be is not yet known. 



So far as the evidence afforded by specimens examined can be 

 relied on, it would seem that the more slender forms known as 

 exilis are comparatively more abundant in the southern portion 

 of the area they are known to inhabit. 



Specimens sent to me by Mr. John Wolf of Canton, Illinois, 

 gave a large preponderance of the shells regarded as suhsolida. 

 Mr. W. not being perplexed by any queries about species, made 

 the very natural suggestion that the more slender shells [exilis) 

 might be males. But be that as it may, the shells in Mr. 

 Wheatley's collection, as well as in my own, very generally 

 testify that exilis and suhsolida are very uniformly associated. 

 They glide into each other by insensible differences in form and 

 size. Other differences they do not appear to possess — or if any 

 are manifested they are evanescent. The bibliographer may 

 decide which of the two names given to the species — exilis, suh- 

 solida — shall be retained. 



Melantho [Pal.) lima, Anth., as represented by the single 

 specimen in Mr. Wheatley's collection, is a well characterized 

 species, which has no decided affinities to group it elsewhere 

 than with 31. DeCanipi. 



Mr. Wheatley's collection illustrates some of the local influ- 

 ences which at the South give a geniculate character to Melantho, 

 just as in Michigan influences of a local character conspire to 

 impress some species with a clavate, others with a gibbous, form. 



