44 



THE MUSEUM. 



cies of lo may be found described and 

 figured in various works treating on 

 the shells of North America, and there 

 is considerable diversity exhibited in 

 their forms, sizes, colors and mark- 

 ings. There seems to be considerable 

 difference of opinion among persons 

 who have studied these shells as re- 

 gards the number of species. There 

 are some individuals who with appar- 

 ent good reason believe that there is 

 really only one species of typical lo, 

 to which all the forms are subordinate 

 as varieties; while on the other hand 

 we shall find others who for reasons 

 quite as good insist that there are five 

 or more "good species." 



The shells, taken by themselves, 

 without regard to any facts relating to 

 their habits, do not afford conclusive 

 testimony as to species, as it is exceed- 

 ingly difficult to isolate forms that 

 cannot be made part of a continuous 

 series when large numbers of shells 

 are placed together. There are, how- 

 ever, some facts connected with geo- 

 graphical distribution and the associa- 

 tion of various forms, which seem to 

 indicate conclusively that there are 

 certainly two species; and, this being 

 admitted, the logical inference might 

 be, under all the circumstances which 

 remain unconsidered, that there are 

 more than two species. This, how- 

 ever, is a question which remains to 

 be investigated. The facts upon which 

 two species are inferred are the fol- 

 lowing: At Black's Ford, Clinch Riv- 

 er, Anderson County, Tenn., two 

 forms of lo constitute very nearly all 

 that are found at that particular local- 

 ity, and these two forms occur there 

 in about equal numbers, and there are 

 not associated with them any inter- 

 mediate forms uniting the extremes. 

 Thirty or forty miles down the river 

 (following its winding course), at Wil- 

 liams' Ford in Roane County, those 

 same two forms reappear, but their 

 relative numbers have changed. At 

 this point the form which seems to be 

 identical with a shell figured by Reeve 

 as lo turrita fnot Mr. Anthony's spe- 



cies of that name, by any means) is 

 the shell occurring in lowest numbers, 

 while the prevailing form is a graceful, 

 slender variety of the shell that Mr. 

 Lea calls spinosa. The change in the 

 relative abundance of two forms by a 

 change of station seems to afford evi- 

 dence relative to species. In follow- 

 ing out the train of ideas which this 

 suggests, it is perhaps appropriate in 

 this connection to glance at the sub- 

 ject of geographical distribution as it 

 relates to other forms, and suggest 

 some of the conditions that seem to be 

 correlated to the diverse forms. A 

 little reflection will satisfy the most 

 casual observer that the conditions 

 under which lo is found are subject to 

 variations of no small magnitude. 



First to be considered is the climat- 

 ic condition, affected by the combined 

 influences of latitude and elevation, 

 conspiring in the northern limit of the 

 region inhabited by lo to produce a 

 lower mean annual temperature than 

 may be inferred at the southern limit. 

 There may be in all a difference of 

 four or five' €egrees of latitude, and 

 possibly from^ two hundred to four 

 hundred feet difference in elevation. 

 In the northerii portion of the area in- 

 habited by lo are found those forms 

 destitute of spines, associated with 

 others in which the spines are only 

 rudimentary or reduced to mere tuber- 

 cles. To the southward, the smooth 

 forms diminish in numbers, and dis- 

 appear entirely before the central lat- 

 itude of Tennesee is reached, and as a 

 warmer climate is approached the de- 

 velopment of the spines becomes more 

 and more luxuriant. This is true of 

 the Holston River in \'irginia and 

 Tennesee, and recent observations have 

 detected a similar state of facts in the 

 Clinch River and its tributary, Powell's 

 River. Besides the influences of cli- 

 mate dependent on latitude and ele- 

 vation, it may be conjectured that 

 there are other influences affecting lo, 

 some of them in a considerable degree 

 depending on the animal properties of 

 the water due to the variable qualities 



