OF PLANORBIS AT STEINHEIM. 39 



such as are described farther on are extremely rare, but still do occur occasionally, though 

 they can only be determined when the young can be seen as in natural sections. 



PI. tenuis occurs quite frequently, and also a variety, -which is slightly tiirretted. The 

 young are a little flattened, and have narrow imibilici on the lower side, so that they 

 can be at once distinguished. The upper side, and the form as a whole, resembles fig. 

 6, line c, pi. 1, but the lower umbilicus is much narrower, and there are no marks 

 of sulcations. There is one specimen of the young of this species with no umbiUcal 

 depression in the upper side, a truly turretted variety, which resembles precisely the 

 figure of PI. Lartetii Noul., as figured by Sandberger, on the upper side, but is more 

 rounded on the lower side. 



Lymneus socialis, of large size, was very abundant in places, occupying the rock 

 to the exclusion of other forms. GilUa utriculosa Sand., was present in considerable 

 numbers, in the forms figured by Sandberger. Casts of the stems of Chara appear, but 

 are rare. 



The rocks which I have called the Ujiper Tier, form the summit of the crest, 

 and like those of the Lower Tier are much denuded, the surfiice being Avorn out 

 into pillars of fantastic shapes, and rough looking knolls. The composition is similar 

 to that of the Lower Tier, but much harder and denser in places, though nowhere is 

 the porous characteristic, formerly described, entirely lost. The fossils are much less 

 numerous than in the Lower Tier with the exception of the Chara stems which are 

 very abundant in some places. 



PI. discoideus is very rare, but PI. ^'fenuif is of more frequent occurrence. PL tenuis 

 is the most abundant fossil, but is almost wholly represented by the very flat form, which 

 is quite rare in the Lower Tier. The slightly turretted variety, Avhich is quite common 

 in the Lower Tier, is found here also, but is much more infrequent. All the specimens 

 are very small or young, with the exception of PI. tenuis. 



Several young specimens were collected, which were identical with those previously 

 described in the Valley Rock as the young of PL steiuiL^mensis- These are here unquestion- 

 ably the young of forms which in the adult have the characteristics of PL tenuis. Never- 

 theless these young have rounded whorls and open umbilici on the lower side, until a much 

 later stage of growth than that at which the angular whorls, etc., are usually acquired in 

 PL tenuis. One full grown specimen was similar to Sandberger's specimens of PL levis, 

 to my PL '""•'tevS"% and also similar to the specimens figured on pi. 1, line b, figs. 13-15. 

 Its evidence makes the relation of the most extreme forms of Steinheimensis and PL levis 

 very clear. It has the peculiar flattened aspect on the upper side and shallow umbilicus of 

 many forms of Steinheimensis with the whorls on the outer and lower sides exactly like 

 those of PL "■"■^/fri"""- Besides these, several young specimens occurred, which were not 

 separable from the young of PL '""■'il'"^"^ , and were undoubtedly identical with them. 



Lymneus socialis of large size is present, but quite rare. In one hand specimen of a 

 peculiar gray limestone on the lower border of the Upper Tier on the west side of the 

 Cloisterberg, were found several specimens and fragments of Pupa antiqua, and a broken 

 cast of a specimen of Helix. A fragment of a tooth with thick dark-brown enamel, like 

 that of some small rodent, was also found. 



