Groups of Uucertain Affinities 195 



separated from the body whorl, a thick callus on the parietal wall and 

 the outer lip thickened in many specimens. 



Horizon and Distribution. ^Miocene period. Steinheim near Heiden- 

 heim, Wiirttenberg, Germany. 



Remarks. The planorbid fauna at Steinheim has become classical for 

 studies of variation, not only as individuals in a fauna, but also in time 

 between the earlier and later strata. Perhaps Hyatt's studies in 1880 (pp. 

 1-114, plates 1-9 » are the best known and show in large measure the great 

 amount of variation which has taken place during the life of these mollusks 

 while the Tertiary strata w^ere being formed in the old lake bed and on its 

 shores. Hyatt refers all species to the genus Planorbis. 



In a later paper (1920, pp. 155-216, Taf. 10-12), Gottschick reviews 

 what is known concerning the fossils of this locality. He postulated a cold- 

 Avater fauna and a warm-water fauna, as we sometimes find in the Pleisto- 

 cene faunas of the middle west. This paper is well illustrated and shows the 

 great variation in the group of shells known as Planorbis ))iultiformis. 

 Wenz (1923, p. 1601 1 includes all of the Steinheim fossils in the genus 

 Gyrauhis. The work of Wenz also brings out clearly the fact that the 

 fossils of this and nearby regions have been very much overnamed, for 

 between 1824 and 1920 no less than forty-five names have been given to 

 variations of this group. 



A careful study of the works of Hyatt, Gottschick, and others shows 

 that, while many of the so-called species appear to be referable to the 

 genus Gyrauhis, the forms grouped around multiformis (trochiformis) 

 appear different from the Gyraulus-like shells, approaching Valvata in 

 form, and apparently should be segregated in another group. Morch, in 

 1863, recognized this difference and gave the assemblage the name of 

 Poecilospira. Later authors appear to have overlooked this name which 

 does not appear in recent monographs or check lists. It is not mentioned 

 by Wenz (1923) in the list of fossils related to trochiformis. 



To what group Poecilospira is related is not definitely clear. It is cer- 

 tainly not near Gyraidus and apparently does not belong in the subfamily 

 Planorbinae. Also, it is not related to Carinifex or to any of the fossil 

 relatives of this group. There are some features in common between 

 Poecilospira and Choanomphalus and its true position may be with the 

 latter group, as suggested by Tryon in 1884. 



