The Mollusca ok Eastern Io\va. 57 



be reserved until a much more careful comparison of the 

 shells, and in the Gasteropoda, of the dentition can be made. 

 While we do not regard dentition of itself as sufficient to de- 

 termine species, it certainly should be taken into consideration 

 with other characters. No reference to the dentition is made 

 in these notes because much of the material in our possession 

 has not yet been worked out and the notes would necessarily 

 be fragmentary. 



No descriptions of species are attempted but attention is 

 given rather to the variation in the characters of some species, 

 and to habitat. The majority of the forms listed were collected 

 and studied by the writer, but where notes were obtained from 

 other sources due credit is givem under the species. The 

 comparison of notes with Prof. F. M. Witter's "Mollusca of 

 Muscatine Co.," proved to be especially interesting, as did also 

 the study of specimens donated to the University by Prof- 

 Witter. 



CLASS— GASTEROPODA. 



SUB = CLASS — PROSOBRANCFIIATA. 



Order — Pectinibranohiata. 



FAMILY -STREPOMATIDiE. 



Genus Pleurocera. — Raf. 

 P. SUBULARE. — Lea. 



Very common in the larger, rocky streams. Usually found 

 near the shore on rocks which are covered with a thin layer 

 of mud. The coloration and sculpture vary. Some forms are 

 light horn-colored, others of a deep purplish brown. Some are 

 almost smooth, others with sharp spiral lines. The latter has 

 been received by us labelled P. lezuisii. 



On the whole the variation is such that if the rule which has 

 been adopted by conchologists for the classification of south- 

 ern Strepomatidce should be applied several species (?) could 

 be estabHshed. 



