88 PALEONTOLOGY OP NEW- YORK. 



often rising in ridges which in the exfoliated shell do not show the divi- 

 sions. Some specimens have the striae sharp and slender, and nearly 

 equal, with wider plain intermediate spaces. On the dorsal valve the 

 atrial are pretty uniform ; the stronger ones being distant, sharp and 

 elevated, with wide intermediate spaces marked by extremely fine regular 

 ■triaj, from the midst of which, as the shell increases, the elevated striae 

 arise, dividing the space in which the smaller striae are constantly in- 

 creasing by intercalation. 



The modifications in the expression of the surface strisB, in the specimens, are represented 

 OB Plate XI, figures 25, 20, 30 & 31, and on Plate xiii, figures 6-8. In the lattet 

 figures the striae are uneven, and rise in ridges with irregular interspaces. 



In figure 29, Plate xi, which is a oast of the ventral valve, there are regular interspaces 

 between the fine elevated strias, a character more usually observed in the dorsal valve. 



The muscular impressions of the ventral valve show narrow elongate scars for the occlusor 

 muscles, and the divaricator muscular impressions are spreading, flabelliform, and deep- 

 ly striated. In many of the oasts, the lower part of the specimen is marked by strong 

 vascular impressions, which are shown iu figures 26 & 27 of Plate xi. The muscular 

 impressions of the dorsal valve are narrow and elongate, and the cardinal process is 

 usually comparatively slender. The interior surface of the valves is granulose or pu- 

 Btulose. 



This species approaches the S. patersoni; and in some specimens, it is not easy 

 to decide the specific diflferences. In the latter species, the muscular impressions 

 of the ventral valve are smaller and shorter, while the wide interspaces between 

 the stronger striae on the ventral valve are characters not observed in any of the 

 numerous authentic specimens of S. inequiradiata : at the same time, there are 

 many obscure specimens in the Schoharie grit and Corniferous limestone, which 

 it is difficult to refer satisfactorily to either of the species described. 



The S. inequiradiata is entirely distinct from the S. inequistriata of Conrad, with 

 wkioh ft has been sometimes united*, as will be shown under the description of 

 that species in the Hamilton group. 



Geological formation and locality. In the Schoharie grit in Albany and Scho- 

 harie counties ; and in the Corniferous limestone of the Helderberg mountains, 

 Schoharie, Cherry-valley, and other places. 



* It ii perhaps unfortunate that the name has the same sign!0cation. 



