of tlie subject. Tliis, on more intiinatc acquahitrcncc, trill 

 prove its greatest charm and a tremendous atimnlant to exer- 

 tion, Tiic difliculty generally is to knoxn how to hegin. My 

 first attempts were devoted to mere collecting in both fossi? 

 and recent conchology. I accnmulated vast numbers of spec- 

 imens, which I endeavored to arrange and classify. It wa» 

 slow work at first. And I desire here to express my gratitude 

 to an old friend who relieved my i>erplc.\ities and encouraged 

 Tue to further labors. I refer to Dr. L, N, Dimmick, now of 

 Santa Barbara, California. 



In regard to the species of Mollusca found m this county 

 the mmibcr may seem large when we consider the geograph- 

 ical limits. And yet I am well aware that all arc not enumer- 

 ated in this paper. The list is, however, very respectable, and 

 shows not only the interest attaching to this field but indicates 

 that there remain additional facts and species to be investi- 

 gated. I have taken the ntmi^st pains to have this }>aper free 

 from errors. jNIy descriptions of species are intended to be 

 short, plain and concise, embracing, j>erhap», parts of those 

 used by the authors. l>ut species vary with their localities. 

 This is illustrated in several descriptions of Thomas Say. One 

 species of our La Salle county univalves also exhibits import- 

 ant modifications. In this paper my groupings are based 

 mainly on the latest authorities in Ihi^ country. For the 

 purpose, I have consulted Binney and Bland's " Land and Fresh 

 Water Shells." I have also looked over the *' Invertcbrata 

 of Mass.," by Gould and Binney; and examined the new 

 grouping of X. A. Ilelicida^ proposed by Bland and Binney, 

 in their paper of 1872. I have used most of the Subgenera as 

 they now stand. I do not, however, attach great in)portancc 

 to this matter .'is I regard the present systems as transitional, 

 and until the anatomy of all the species is thoroughly known, 

 they must remain so. In the F^amily Cycladidiv, I have fol- 

 lowed Prime. And in the Family Uiuonidu>, Dr. Lea. The 

 latter Family aflbrds an inviting field for making genera and 

 sub-genera among some of the species. Btit I am not prc- 

 l)ared to entov upon a Avork of this nature. Were a person 

 writing up all our species it would l)e advisable to makcsomv 



