have devised numerous ingenious ones. We use a set of 10 to 20 small 

 artist's color pans, round, 2 inches in diameter, to hold the kinds of shells 

 sorted from our samples; we do the sorting in a Petri dish, a glass dish 

 4 inches in diameter in which the shells can be separated from the debris 

 with brushes. We pick up the larger shells with tweezers and the smaller 

 ones with fine brushes moistened as needed. 



The next two steps are not strictly collecting and as such should not 

 be described at length in an article on collecting, but they may be men- 

 tioned briefly here as they give the collector the fullest benefit from his 

 collecting. Once the species are identified they provide a record of their 

 history in the particular deposit studied. This may show that some species 

 came in earlier than others; that other species died out before the end of 

 deposition in the lake or pond studied; and that still others were very 

 scarce at first and more abundant in the upper layers. These variations 

 have their significance in interpreting the change of conditions within the 

 area and around it. For example, many lake deposits contain land snails, 

 washed in from the surrounding areas by streams. Their relative abundance 

 in each stage of the lake, represented by the successive slices of material 

 from the muds of the lake bottom, give interesting information on the 

 development of the land area surrounding the lake. Examples of the infor- 

 mation acquired in this way are given in papers by the writer (La Rocque, 

 1952) and Reynolds (1959). 



Identification of inland Pleistocene Mollusca presents some difficulties 

 but some references can be used to advantage. A few are listed below. For 

 example, Pilsbry's m.onograph (Pilsbry, 1939-1948) can be used for land 

 snails and F. C. Baker's (1928) paper on Wisconsin Mollusca and his later 

 publications for freshwater forms, although the nomenclature in the former 

 needs considerable revision. Correspondence with a specialist will clear up 

 many points and the writer will be glad to oft'er what help and advice he 

 can give to those interested. 



REFERENCES CITED 



BAKER, FRANK C, 1928. The Fresh Water Mollusca of Wisconsin. Wis. Geol. 

 and Nat. Hist. Survey, Bull. 70. pt. I, 494 pp., pt. 2, 482 pp., 105 pis. 



LA ROCQUE, A., 1952. Molluscan Faunas of the Orleton Mastodon Site, Madison 

 Countu, Ohio. Ohio Jour. Sci., vol. 52, pp. 10-27. 



PILSBRY, HENRY A., 1939-1948. Land Mollusca of North America {North of 

 Mexico), 2 vols., 994 and 1113 pp., illus. 



REYNOLDS, MARTIN B., 1959. Pleistocene Molluscan Faunas of the Humboldt 

 Deposit, Ross County, Ohio. Ohio Jour. Sci., vol. 59, pp. 152-166, 6 figs. 



COLLECTING MOLLUSKS IN DESERT REGIONS 



By Ernest J. Roscoe 



Chicago Natural History Museum, Chicago 5, Illinois 



Introduction. Success in collecting mollusks in desert regions depends 

 largely upon (1) a knowledge of the desert environment and (2) a famil- 

 iarity with the ecological requirements of these animals. This is true of 

 collecting in any environmental type, of course, but is especially applicable 



(72) 



