LOWER HELDERBERG ROCKS. 
SOS 
subsequently obtained, show that the fossils having the character just 
noticed possess a peculiar form of columella, which is more or less dis¬ 
tinctly twisted or folded, or with a broad spiral groove within the outer 
edge of the columella, and between that and a parallel ridge or callosity. 
For these shells I propose the generic name Strophostylus. 
Genus Strophostylus (n. g.). 
[ Gr. ( frpstpu , verlo ; ffrvXog , columella .] 
Generic character. Shells subglobose or ovoid-globose. Spire small, with 
a large ventricose body-whorl; outer lip thin, not reflected (sometimes 
slightly expanded); columella twisted or spirally grooved within, not 
reflected; umbilicus none : aperture somewhat round-ovate or trans¬ 
versely broad oval. 
When the attention has been once called to these forms, there is usually little 
difficulty in distinguishing them from all the other genera by external characters 
alone. The columella is rarely seen, though I have been so fortunate as to discover 
it in three species from the Oriskany sandstone; while it is partially exposed in two 
other species, one of which is from the Oriskany sandstone, and the other from the 
limestone of the Lower Helderberg group. 
1 . 2 . 3 . 
The figures 1 and 2 are illustrations of a well-marked species from the Oriskany sandstone. 
Fig. 3 is of another species from the same rock, showing the same general character of the 
columella. 
