THE 



AMERICAN NATURALIST. 



Vol. xvi. — JUNE, 1882. — No. 6. 



TRANSFORMATIONS OF PLANORBIS AT STEINHEIM. 



WITH REMARKS ON THE EFFECTS OF 



GRAVITY UPON THE FORMS OF 



SHELLS AND ANIMALS. 1 



BY ALPHEUS HYATT. 



TN continuation of our review in this journal for October last 

 A (P- 793) of Professor Hyatt's contribution to the evolution the- 

 ory, we make the following extracts from his last condensed paper, 

 and reproduce from the Proceedings of the American Association 

 the plates illustrating the paper. The results of his studies on the 

 Steinheim shells are roughly exhibited on Plate vi, and may be 

 described briefly as follows. Figs. 1,8, 12 and 16, are the ances- 

 tors, varieties of Planorbis levis from the older Tertiaries of another 

 locality, identified, named, and kindly sent to me with eleven 

 other specimens of this species by Professor G. Sandberger, 2 who 

 opposes the evolutionary conclusions of both Hilgendorf and 

 myself. 



From these four varieties spring four distinct lines of descent. 

 Fig. I begins the series from 2-7, in which of course numbers of 

 the connecting forms are not figured. Fig. 8 begins the series 

 from 9-1 1, much shorter and containing fewer forms than in series 

 j£7- Fig. 12 also gives rise to a short series with only few forms. 

 F'g. 16, however, is the starting point for a compound series, or 

 one composed of at least three sub-series, 19-20, 2 [-24, and 25-28. 



The intermediate forms by which the gap between the four 



^From the Proceedings of the American Association for the Advancement of 

 •Man, Vol. xxix, Boston Meeting, August, 1880. 



