12 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 



Succinen grosvenori gelida of Baker, although it occurs at many places with 

 Succinea grosvenori Lea, has nowhere been observed to intergrade with the kind of 

 shell here treated as acceptable grosvenori , and is likewise treated as a full species 

 and called Succinea ielida. It should be remarked that the names Succinea gelida 

 and S. grosvenori are here used in the sense of "form" species, inasmuch as it is 

 virtually impossible to distinguish many species of Succineidae from the shells 

 alone. It is therefore difficult to assess the value and significance of the variations 

 seen. Wayne's (1959, p. 11) remark, "Only .. .Succinea ielida is known at this time 

 to have stratigraphic application in Indiana, " probably reflects the difficulties en- 

 tailed in distinguishing among different species of the smaller kinds of Succinea 

 and related genera . 



Farmdalian Faunas 



Farmdalian molluscan faunas in the area under consideration are not yet well 

 characterized. Only three localities (8, 24, 57b) are known, and each of these is 

 atypical in some manner or other. Locality 8 (the Wedron section) exposes, among 

 other sediments, 25 feet of dark gray silt with some clay and sand streaks from which 

 an abundant molluscan fauna was recovered. A radiocarbon date in the upper third 

 of this unit clearly places the deposit well within the Farmdalian, but the fauna, 

 composed exclusively of aquatic species, does not present a complete picture of the 

 total assemblage living in the area at the time. 



The collections from the Lake Bloomington Spillway section (locality 24) have 

 been referred to the Farmdalian fauna because of their general resemblance to those 

 at the Wedron Quarry section and in spite of two contradictory radiocarbon dates. 



The third locality (57b, "The Rocks" section), judged by lithological rela- 

 tions and radiocarbon years (22,200 ± 450; W-867), is transitional between the 

 Farmdalian and Woodfordian substages, but the mollusks contained in bed 4 of the 

 geologic section are so unlike those in the overlying Peoria loess that they are as- 

 signed to the Farmdalian assemblage. The fauna here bears a strong resemblance 

 to that of the Altonian, but differs in the presence ofTriodopsis foster i rather than 

 T. hubrichti, and in the predominance of Anguispira kochi , which is relatively rare 

 in Altonian deposits. For reasons not readily apparent, almost all the species here 

 are represented by individuals that are larger than usual, each approaching or oc- 

 casionally exceeding the upper limits of the ordinary range in size. This observa- 

 tion is especially true of A I logona profunda , Anguispira alternata, and A. kochi. 



With these reservations, the Farmdalian molluscan fauna as now known from 

 these localities consists of 24 species. Six of these, Anguisvira alternata, Haplo- 

 irema concavum f Hendersonia occulta, Stenotrema fraternum , S. hirsutum , and 

 Succinea ovalis range from Altonian through the Woodfordian Substages; in fact 

 they are generally more abundant in Woodfordian deposits than they are now known 

 to be in the Farmdalian. A second group of species, including Gyraulus altissimus , 

 Lymnaea dalli , L. obrussa dec amp i , L. parva , Helisoma antrosa , Pisidium compres- 

 sum , P. caseratanum , Triodopsis fosteri, andValvata tricarinata are known to occur 

 in Woodfordian and Farmdalian assemblages. Two species, Allogona profunda and 

 Anguispira kochi, occur in the Altonian as well as the Farmdalian but have not been 

 seen in Woodfordian collections in the area under consideration. 



Finally, a group of species, conspicuous among which is Amnicola leightoni, 

 A. lustrica Gyraulus cristus, Lymnaea palustris , Sphaerium striatinum, and Valvata 

 sincera found only in Farmdalian faunas. 



