GASTEROPODA. 
31 
The slight thickening and fold in the columellar lip distinguish this as a 
Stropiiostylus, while there is no indication of an umbilicus. The form of this 
shell differs little from Platyostoma linPaia; but the even convexity of the spire, 
and the absence usually of revolving striae, are distinguishing external features, 
j Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 
Stropiiostylus varians. 
PLATE XI, FIGS. 16-31. 
Stropiiostylus varians, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 11. 1876. 
Shell obliquely subconical, or depressed subglobose. Spire moderately ele¬ 
vated ; volutions about three or four, symmetrically rounded above, and 
somewhat gradually enlarging to the last one, which is very ventricose, 
extending downward and forward. Aperture ovate or suborbicular; 
peristome entire; the columellar lip usually expanded and spreading 
over the umbilicus, sometimes free, and leaving the umbilicus exposed. 
Surface finely striate, with the peculiar thread-like striae visible on well- 
preserved surfaces, while, on the weathered portions, they become lamel- 
lose; and on some specimens the surface is marked by peculiar waved and 
interrupted striae (shown in fig. 18). 
This species, in some respects, makes a wider departure from the typical 
forms of Stropiiostylus than any other of the genus known to me. The peculiar 
and characteristic form is preserved ; the symmetrical rounding of the volutions 
above, and the delicately formed spire, as well as the form of aperture in some 
specimens, are all characteristic of the genus. The striae, however, have a 
tendency to become lamellose, or interruptedly undulating; and there are 
evidences of irregularity of growth and indentations in the margin of the 
peristome (indicated in figs. 24 and 25), both above and below the periphery. 
The form of the aperture is extremely variable, from narrow elliptical to 
broadly expanded. There is (rarely shown) a tendency in the last volution to 
become free (fig. 23), and the characteristic plication of the columellar lip is 
