26G Till. CHICAGO ACADEMY OF SCIENCES. 



FLORENCIA FORMATION. 

 [LLINOIS: Indian Garden, Pecatonica River Valley, Stephenson Co. (Her- 

 shey). 



Various Pleistocene Formations. 



united states. 



California: Walnut Creek, Contra Costa Co.; Tassajora Lake Bed? 

 deposit near Walnut Creek, Alameda Co., north of Livermore. (Cooper; . 



Iowa: Drift of Iowa (Udden). 



Michigan: Near Buchanan, Berrien Co., with Mastodon remains (Smith) ; 

 with Mastodon remains, Niles, Berrien Co. (Walker). 



Nevada: Upper Lahontan beds, Rye Patch, Humboldt Co. (Call). 



New Mexico: Dry Salt Lake, near Eddy, Eddy Co. (Sterki). 



Texas: Forks of Groesbeck Creek, three miles west of Quanah, Hardeman 

 Co.; 



"Rush's pasture, Wild Horse Creek, northeast of Big Spring, Howard 

 Co., northwest Texas, from bed of sandy clay, twenty feet above present bed 

 of creek. The bed rests upon a conglomerate composed of small silicious peb- 

 bles. Found with mammalian remains" (Singley). 



BRITISH AMERICA. 



Ontario: Fossiliferous sands overlying the clays of Essex Co. (Stearns). 



Ecology : Modicella usually selects as a habitat a mud flat or a 

 strip of muddy beach which is kept rather moist. In such a situation 

 it has been seen by the writer in Wisconsin, Illinois, Indiana, New 

 York and Pennsylvania. It has also been collected from boards, sticks 

 and other debris along the shore. At Alpena, Michigan, it was col- 

 lected by Dr. Nason on a broad, sandy beach near the outlet of Long 

 Lake, in from six inches to a foot of water. The shells are very thick 

 and well illustrate the effect of rough water. Mr. Woodruff records 

 the habitat in southern Illinois as follows (Nautilus XI, p. 28) : 



"The shells were found in a rocky glen or cleft in the center of 

 the chain of high precipices known by the names of Fountain Bluff, 

 Devil's Bake Oven and Backbone. This cleft or ravine begins about 

 three-quarters of a mile from the face of the cliff and gradually de- 

 scends in a northwesterly direction until the bottom is reached, and 

 one may stand upon a broad shelf of rock ten feet from the ground, 

 with high overhanging cliffs of bare rock on both sides. A stream 

 of clear spring water flows down this ravine and, falling over the high 

 shelves of rock, has formed numerous round pools or basins. I was 

 surprised to find no shells in the stream, and could only collect a few 

 specimens of Limncca humilis, which I found clinging to the wet moss 

 under the falls." 



Remarks : Modicella is closely related to humilis, differing in 

 having a longer and narrozver aperture and a less obese body whorl; 

 in the majority of individuals the upper extremity of the lip where 



