322 Notes on the MoUuscan Fauna oj Northern Illinois. 



the distributiou of species in the State, their classification , etc. It is 

 probable that nearly all the American terrestrial species have been 

 described. But much work yet remains in the department of aquatic 

 moUusca in rectifying past errors, eliminating synonyms, and fixing the 

 geographical limits of species. The latter has now become the most 

 important matter claiming the attention of the naturalist. We may 

 not presume to see many new species added to the already formidable 

 list, but we shall have the position of those now imperfectly known 

 more fully settled ; and we may expect to see several of Thomas Say, 

 which are at present classed among the synonyms, restored to their 

 proper places as species. In regard to the classification and grouping 

 of species, we may consider the present systems as transitional. Some 

 species now treated as subgenera, will, when that ceases to W'ork, be 

 treated as genera. The family Unionidaj will be revised, and new 

 groupings arranged, more in accordance with the common characters 

 among some of the members. The Strepomatidse will afford a fruitful 

 field of investigation for some time to come. This family presents the 

 most remarkable study in the wdiole range of American conchology. 

 When we reflect that nearly five hundred species have been described, 

 and about ninety jjcr cent, of these from waters south of the Ohio 

 river, we can form some idea of the varieties in this single group of 

 the mollusca. Not less interesting are Melantho and Vivipara. From 

 them we may hope to establish seven or eight permanent species. 

 Though the process of future study and research will no doubt cut 

 down the number of species, yet enough will remain to demonstrate the 

 extraordinary development of American molluscous life. The following 

 are common to the northern half of the State of Illinois : 



Family Helieidce. — Genus MacrocycUs — (Beck). ^ 

 31. concava, Say. This carnivorous species is very abundant and of 

 large size. 



Genus Zonites — (Montfokd). 



Z. arboreus, Say; Z. viriduhts, Menke. Z. fulva, Drap. Z. cellaria, 

 Muller. The latter is an introduced species, and found in great num- 

 bers around greenhouses where foreign plants are kept. It is the same 

 no doubt as H. gla2)hyra, Say, Z. minuscula, Binney. Not abundant, 

 so far as I have observed. Z. lineata, Say ; abundant. 



Helicince. — Genus Putula — (Halde) . 

 H. alternata, Say. H. alternata — a variety resembling mordax. H. 

 solitaria, Say, H. striatella, Anth. H. ]}crspectvva, Say. All the pre- 

 ceding, except the last two, are very abundant. 



