CONTRIBUTIONS TO PALAEONTOLOGY. 41 



PLATYOSTOMA STROPHIUS ( n. s.). 



Shell obliquely ovoid. Spire ascending, composed of about three or 

 four volutions : apex minute; volutions very gradually expanding 

 above; the body-whorl ventricose, somewhat depressed-convex on 

 the side, and sloping downwards rather than swelling out in a 

 rotund form; the upper volutions standing out prominently above 

 the last one. Suture-line narrow, even, and sometimes appearing 

 as very narrowly and deeply canaliculate. 



Surface marked by fine concentric striae, which are sometimes 

 crowded into wave-like fascicles or undulating folds, and some- 

 times abruptly bent forwards near the base. In some parts, or 

 upon some specimens, these striae are very regular and even, as 

 in Strophostylus. Aperture ovate, and, in one specimen, with a 

 sinus near the base. 



This species is less ventricose than the P. lineata, and the spire much 

 more elevated, while no revolving lines have been observed. In many re- 

 spects it resembles Strophostylus, but the aperture has not been entirely 

 determined. 



Geological formation and locality. In the Corniferous limestone : 



STROPHOSTYLUS UNICA(n.s.). 



Shell suborbicular ; height and length about as three to four. 

 Spire consisting of three or four volutions; the apex moderately 

 elevated above the outer volution. Suture close, and the volutions 

 evenly convex upon the upper side. Body-whorl ventricose, evenly 

 and equally rounded upon the back. Aperture subovate, a little 

 extended at the lower side and slightly straitened on the posterior 

 side : outer lip regularly curved ; columellar lip thickened and 

 slightly twisted, the fold being near the upper part of the lip. 



Surface marked by fine crowded concentric striae, which are broadly 

 curved backwards on the dorsum : shell very thick. At one point 

 where the shell is broken away, the surface, within the cavity, is 

 marked by revolving strise. 



The slight thickening and fold in the columellar lip distinguish this as a 

 Strophostylus, while there is no indication of an umbilicus. The form of 

 this shell differs little from Platyostoma lineata; but the even convexity of 

 the spire, and usual absence of revolving striae, are distinguishing external 

 features. 



Geological formation and locality. In Schoharie grit : at Schoharie. 

 1861.] 6 [Senate No. 116.] 



