1893.] NATURAL SCIENCES OF PHILADELPHIA. 235 



As with the genus so it was with the species ranged under it. 

 Muller 7 described " Helix " pulchella and costata, and for nearly a 

 century, even up to our own time, almost all writers united them 

 in one species, under one or the other of the two names, generally 

 pulchella, regarding the other form as varietal. The fact alone 

 that the two forms, evidently of very ancient origin like the whole 

 genus, have persisted as such, side by side almost everywhere, over 

 a very wide area, is sufficient to prove their distinctness, not to 

 speak of the really marked differences of the shells. Only in the 

 last decades, however, has this conviction become prevalent ; and in 

 America, Morse (I. c.) was the first to express this opinion. On 

 closer study, conchologists admitted that there are quite a number 

 of other species besides the two " standard " ones. 



But of many of them it is difficult to judge. 1. Their anatomic 

 characters have not, especially the genitalia, been studied suffi- 

 ciently, and it is not known whether they present any specific pecu- 

 liarities 8 apart from those of the jaw and radula. 2. The material 

 at hand, considering the shells alone, is insufficient to allow the 

 formation of a judgment whether certain forms are species, varie- 

 ties, or mere local variations and mutations. 3. The shells in this 

 genus are so uniform in size, shape and color, that it takes careful 

 comparison to become familiar with the forms and their peculiar 

 features, as well as the ranges of variation. 



"When Mr. Pilsbry requested me to study the genus, I knew very 

 little about it, and was disposed to decline. After a conscientious 

 study of the material at hand, and the literature accessible, I 

 believe I have effected something to promote our knowledge of 

 these minute and interesting mollusca. This paper, in the absence 

 of anatomical study and of specimens of many published species, is 

 not a monograph of the genus. It may, however, serve as a guide 

 to further investigations. 



To Mr. H. A. Pilsbry I am especially indebted for much informa- 

 tion, references to literature, etc., and I take this opportunity of 

 tendering him my hearty thanks. 



GENERAL DESCRIPTION. 



Soft parts. — They are, in general aspect, like those of Helix, but, 

 as already pointed out, there is no secondary ureter. A few other 



7 0. F. Muller, Vermium Historia, 1774, pp. 30, 31. 



8 Such difference*, however, may be looked for as probable, as such have been 

 found among nearly related species of other groups; conf, e. g. v. Ihering's book 

 on the genital apparatus of Helix, cited above. 



