May, 1919] Silurian Fossils From Ohio 383 



viewed from the pedicel valve side of the shell. These laterally flattened 

 shells evidently are only individual variations from the much more 

 abundant shells in which the lateral outline is more ovate. In occasional 

 specimens the lateral boundaries of the flattened anterior areas of 

 the pedicel valve are slightly elevated and are bounded on their inner 

 sides by very shallow lines of depression. In such cases, if the median 

 line of depression be present, the anterior half of this valve appears 

 marked by four, rather faint, low plications, somewhat as illustrated 

 by Hall and Clarke. 



The laterally compressed individuals, such as those illus- 

 trated by Meek and by Hall and Clarke, are most abundant 

 in the vicinity of Hillsboro and Danville, Ohio, where they 

 form only a moderate percentage of the more normal broader 

 forms. Half a mile west of Port William, Ohio, on the road 

 to Lumberton, a quarter of a mile south of the bridge, many 

 of the specimens are rather broadl}^ ovate, but a few of the 

 laterally compressed forms occur also. The species is widely 

 distributed in the lower part of the West Union formation 

 in southern Ohio, but usually without any evidence of lateral 

 compression, which seems to be a local feature. 



Specimens closely resembling typical Whitfieldella cylindrica 

 from the Irondequoit limestone of New York, both in size and 

 form, occur also in the Osgood formation of Indiana, especially 

 in the area southwest of Versailles, in Ripley county. Here 

 also the narrower specimens are exceptional and are associated 

 with broader, ovate forms, the latter occurring in much larger 

 numbers. 



Poleumita prosseri Sp. nov. 

 Plate XVII, Figs. S A-C. 



Spire depressed, with the apex rising but slightly above the margin 

 of the outer whorl. Whorls five or six; convexity of upper side of 

 body whorl slightly depressed; convexity of lower side broader and 

 distinctly flattened; umbilicus relatively small and shallow. On the 

 upper side of the body whorl, half way between the suture and the 

 periphery, there is a distinct but low revolving ridge. Along the 

 periphery there is a similar, but much fainter revolving ridge. Between 

 the two ridges just described occur two more, so as to form a series 

 following each other at shorter intervals in a downward direction. 

 Sometimes a fifth revolving ridge may be faintly recognized just below 

 the peripheral line. At the ridges, the transverse striae bend shghtly 

 backward and at the same time rise in prominence, thus producing the 

 appearance of a revolving ridge. Six or seven transverse striee occur 

 in a length of 2 millimeters. The largest specimen discovered so far 

 was 28 mm. in diameter, and had a body whorl 9 mm. in height; the 

 thickness of the shell at the aperture equalled one millimeter. 



