WISCONSINAN MOLLUSCAN FAUNAS 9 



Despite the small number of species restricted to the Altonian, the assem- 

 blage is distinctive and easily recognizable even in the field, inasmuch as the most 

 characteristic species are of large size and most of them occur consistently at most 

 localities. Triodopsis altonensis and Alloiona profunda, both easily recognized, 

 occur most consistently at all of the eleven Altonian localities studied. Although 

 apparently restricted to the Altonian, Triodopsis hubrichti does not occur frequently 

 enough to make it of significant value in faunal characterization. Aniuispira alter- 

 nate also is a conspicuous member of the Altonian assemblage although it ranges 

 throughout the Wisconsinan in the area under consideration. Like Alloiona pro- 

 funda, it occurs at each of the eleven localities studied. 



Ecological Considerations 



The characteristic Altonian molluscan fauna is typical of those occurring in 

 well established hardwood forests, an observation confirmed by the abundance of 

 Aniuispira kochi at some localities. Of A. kochi Goodrich (1932, p. 35) says: 

 " . . .one of the typical mollusks of old forests, and seldom found even in thick 

 second-growth timber. It hides during the hours of bright days under rotting logs 

 and decaying leaves." Of the habits of Triodopsis altonensis nothing is known, 

 but because of its close genetic relationship with T. multilineata it may be inferred 

 that it lived in especially humid portions of forests or forest borders. T. multilineata 

 has been observed living in heavily forested Missouri River bluff situations in north- 

 eastern Kansas, where contact springs along beds of shale keep fallen leaves and 

 leaf-mold constantly wet. Alloiona profunda also is a species of the deep forest, 

 and at many stations occurs with T. altonensis, Succinea ovalis, and Haplotrema 

 concavum along wooded bluff lines. The relation of Aniuispira alternata to wood- 

 lands also is well known, but this species often inhabits forest borders under rela- 

 tively small shrubs. 



The association of Aniuispira alternata, A. kochi, Alloiona profunda, Steno- 

 trema fraternum, S. hirsutum , Succinea ovalis , Triodopsis hubrichti, and T. altonen- 

 sis presents a paleoecological picture of a well watered, heavily forested bluff-line 

 habitat, which in Altonian time was receiving heavy deposits of loess. None of the 

 remaining species in the total Altonian assemblage serves to alter this picture, al- 

 though some species, such as Hendersonia occulta and Pomatiopsis scalaris, oc- 

 curred along stream banks and on low floodplain habitats, and many species, such 

 as Gastrocopta armifera, Hawaiia minuscula , and Helicodiscus parallelus may occur 

 in open prairie situations as well as in woodlands. 



The extremely rare occurrence of some typically woodland species, including 

 Cionella lubrica, Strobilops labyrinthica ,and Zonitoides arboreus is unexplained. 



Taxonomic Considerations 



Inasmuch as the shells known asTriodopsis fosteri hubrichti Baker and T. 

 multilineata altonensis Baker are distinctive enough to be readily recognized, and 

 as each is, so far as known, separated from its typical species by a time, rather 

 than a geographical interval, each is here treated as a full species, and they are 

 called T. hubrichti and T. altonensis. In a later section, the gastropod described 

 by Baker as Vertiio iouldi hubrichti, for the same reasons, is called Vertiio hubrichti 

 The same is true of Triodopsis multilineata alionquinensis Nason, herein called 

 Triodopsis alionquinensis . 



