WISCONSINAN MOLLUSCAN FAUNAS 21 



Pupilla muscorum, Retinella electrina s Stenotrema leai , Succinea gelida, Triodopsis 

 algonquinensis , Vertigo alpestris ought on i, and V. modesta . This assemblage is 

 not unlike those typical of northern localities of the Peoria loess. It lacks Discus 

 macclintocki , which does not occur anywhere inside the Shelbyville morainal front. 

 Columella alticola, Hendersonia occulta, and Pupilla muscorum are abundant, and 

 along with Succinea gelida are the most conspicuous faunal elements of the Morton 

 loess. From the scant evidence available, it is not now possible to distinguish 

 the fauna of the Morton loess from that of Peoria loess in northern Illinois. 



Faunal Assemblages from Richland Loess 



The Richland loess, situated stratigraphically above the earliest Woodfordian 

 moraines, is represented at localities 2, 14, and 22 (fig. 2). The combined assem- 

 blage from these collecting stations totals 12 species: Columella alticola, Discus 

 cronkhitei, Euconulus fulvus , Gyraulus altissimus , Lymnaea dalli , L. obrussa 

 decampi , Pisidium compressum, P. caseratanum, Pupilla muscorum, Succinea gelida, 

 Vallonia gracilicosta, and Vertigo modesta. 



The character of the assemblage is not significantly different from that of 

 those found in the Morton loess or in the Peoria loess of northern Illinois. At 

 locality 22 the loess evidently accumulated on a poorly drained surface, as attested 

 by the presence of three genera (Gyraulus , Lymnaea , and Pisidium) of aquatic mol- 

 lusks. We believe this reflects nothing more than an anomalous local ecological 

 condition. 



Faunal Assemblages from Normal and Metamora Moraines 



At two localities fossil shells were obtained from silt inclusions in glacial 

 till, one in the Normal ground moraine (locality 9) and one in the Metamora ground 

 moraine (locality 13). From the first deposit only a meager series was obtained: 

 Discus cronkhitei , Helicodiscus parallelus , and Succinea grosvenori . The second 

 collecting station yielded eight species, including Columella alticola, Discus 

 cronkhitei , Euconulus fulvus, Pupilla muscorum, Succinea gelida, Vallonia gracili- 

 costa f Vertigo hubrichti, and V. modesta . 



The first of these collections obviously has little significance aside from 

 its unusual occurrence within a till mass; the second closely resembles that from 

 the Morton and Richland loess, or, for that matter, the Peoria loess of northern 

 Illinois. 



The ecological significance of these molluscan assemblages from silt-in- 

 till inclusions is considerable, especially as the shells at locality 13 are abundant 

 and had suffered no discernible damage before our collections were made. Several 

 hundred shells were obtained from a bulk sample of approximately 100 pounds of 

 silt. Inasmuch as the fauna is similar to that found in loesses of the region, in- 

 cluding those outside the Wisconsinan glacial boundary, it is evident that continen- 

 tal glaciation at the latitude of northern Illinois did not have a profound effect upon 

 local climate at any considerable distance from the ice front. As the nearly perfect 

 state of preservation of the shells argues against long transportation from other de- 

 posits, we can safely assume that the gastropods found in the silts lived at one 

 time within a stone's throw of the glacial front. Although well preserved shells 

 were collected from sand and silt streaks in till in northeastern Kansas (Frye and 

 Leonard, 1952), to our knowledge the Illinois localities are the most northerly yet 

 reported to yield from a till mass shells in sufficient numbers to make it evident that 

 the animals were living near the ice front. 



