Loess of Iowa City — Shimck. 353 
mon form. A few fagmentary specimens of young shells from 
the loess of Nebraska are in the writer's possession. They are 
probably young shells of the variety. None have been found 
at Iowa City. 
**SUCCINEA Sp. ( ?). 
A rather large Siiccinea, which has not yet been satisfac- 
torily placed, is quite common on bare mud-fiats along streams, 
and also occurs in the local loess. In some respects it is inter- 
mediate between 6^. avara and 5^. ohliqua, sometimes approach- 
ing the smaller, more slender forms of the latter species quite 
closely. 
The foregoing species are wholly terrestrial in habit, and 
moreover, with few exceptions flourish in comparatively dry 
situations. While all require a certain amount of mioisture 
when active, the lower surface of a fallen leaf, a stick, or a 
stone, even in a comparatively exposed place, furnishes all that 
is necessary. 
The following summary of the preceding notes is of inter- 
est : 
Species found at Iowa City only as fossils 6 
Species found here both living and fossil 19 
Species now found living here, but occurring as fossils in the 
loess of other localities 19 
Species living here, but not yet reported from the loess 3 
Total 47 
These shells represent more than 90% of the fossils in the 
loess, and, the fossil fauna so far as it occurs, is very similar 
to the living surface fauna. The latter is richer in species, 
but this difference may be only apparent. A dlose study of 
the local living fauna shows that species frequently occur iti 
very restricted areas. Dififerent parts of the same slope, often 
but a few feet apart, not infrequently show much variation in 
the distribution of species. When we take this peculiarity 
of distribution of land-shells into account with the compara- 
tively very small total area of all the loess exposures of this 
vicinity, we can readily see that the opportunities for finding 
the recent shells are much better. 
While, as stated, the great majority of the local loess fos- 
sils belong to the prec^eding list of terrestrial forms, a few ad- 
ditional species of aquatic habit are also sparingly found. In 
