The Genesis of the Teetiaet Species of Plakoebis at Steinheim. 



Bt Alpheus Hyatt. 



X HE following work arose from the interest excited in my mind by the brief account 

 of the Steinheim fossils, given by Dr. Hilgendorf, in the " Monatsbericht d. K. Preuss. 

 Akademie d. Wissensch. zu Berlin," for July, 1866. My attention was attracted to this 

 paper soon after its publication, because, if true, it was the only reliable statement of the 

 theory of evolution, which could be considered a demonstration of the practical applicability 

 of that doctrine to the life history of any considerable series of animal forms ; and as by 

 previous studies I had tried to prepare for the appreciation of such problems, it was with a 

 feeling of most intense pleasure that, in 1872, I found myself in the neighborhood of this 

 famous locality. 



Through the introduction of Prof. Fraas, of Stuttgart, I was enabled to make my 

 investigations and pursue my studies with every flicility. During the first visit, as the time 

 was limited, and it was somewhat late in the autumn, the work was confined almost wholly 

 to the survey of the pits. A hole was dug in the Old Pit, down to the dark brown clay 

 which forms the base of these deposits. Specimens were collected in abundance, by the 

 bag-full, without regard to what they might be, and secured on the spot in paper bags and 

 boxes containing labels, indicating, by a prearranged system of notation, the precise level 

 from which they came. Not anticipating any new or original results from the work, 

 I was simply careful to obtain unmixed samples from every stratum and the intermediate 

 partings of limestone. After the return to Cannstadt, where I was then residing, a large 

 part of my leisure during the winter was spent in sifting the material, picking out the 

 shells, studying and drawing with a camera-lucida the diiferent varieties, making one 

 hundred and eighteen drawings in all. 



The process of examination was conducted as follows : The bags were opened one at a 

 time, according to their formations. The contents of each bag was sifted by a series of thi-ee 

 graded and nested sieves, made for the purpose, over a large plate or basin. These 

 allowed only the fine dust to escape into the dish. All of the four lots, thus divided 

 according to their sizes, were examined at each operation, and the shells found secured in 

 pill-boxes, marked with the same label as the bag ; after each bag was finished a general 

 examination was made, and the species of each separate bag compared with others, even if 

 they came from a spot only a foot or a few inches removed. 



In this way the greatest attainable security from any accidental mingling was obtained, 

 and the contents of separate bags, even from the same formation, were never mixed until 



