Na(uial History Notes frotn North Carolina. 209 



NATURAL HISTORY NOTES FROM NORTH 

 CAROLINA. 



Bv A. G. \Vi:thekby. 



Number Two. 



TIIK L.\ND SHKLLS OF ROAN MOUNTAIN AND VICINITY, 

 CONTINUED. 



The foregoing nine species have been grouped, with others, 

 under Mesodon (Rafinesque, 1831), but whether the group is 

 to be regarded as a genus, subgenus, or section, the system- 

 atists have left us in doubt. " Binney (Bull. U. S. Nat. Mus., 

 No. 28, p. 295), calls it "a genus strictly North American," 

 but on the same page, a little farther on, says, " Nothing has 

 been published regarding the jaw and lingual dentition of the 

 subgenus^ etc., thus making the group both generic and sub- 

 generic on the same page ! In the farther discussion of this, 

 division, he again uses the term genus. This section has 

 affinities with Triodopsis (Rafinesque, 1819,) on the one hand 

 and with Steiioirema (Rafinesque, 181 9,) on the other. As it 

 is difficult to draw the lines which wnll separate man}- of the 

 so-called species in these groups, so is it difiicult to make any 

 complete generic or subgeneric separation. The passage 

 from Triodopsis into Mesodon on the one hand, through 

 such forms as subpalliata and appressa into dentifej'tis and 

 roemeri, and on the other through monodon and geriiiana into 

 M. lawi, mobiliana 2inA Jejuna, is so gradual and complete as 

 to obliterate generic or subgeneric division predicated upon 

 the shell alone. 



Still less dependence can be placed on the characters of the 

 jaw and lingual ribbon. So great is the difference of these 

 organs, even in individuals of the same species, that the true 

 wonder is how so much "systematic" work has been based 

 upon them. The most hurried analysis of authors' results, as 



