OBSERVATIONS 



Upon some new and other species of Fossils, from the 

 rocks of Hudson-river group of Ohio and the Western 

 States ; with descriptions. 



[Continued from page 121 of the 13th Annual Report of the Regents of the University on the 

 State Collections of Natural History.] 



ORTHIS JAMESI (new species). 



Shell transversely semielliptical : hinge-line equalling, or a little 

 greater than the width of the shell below ; the length a little 

 more than half the width, and sometimes nearly two-thirds. 

 Cardinal extremities compressed, and usually truncate or 

 rounded. Dorsal valve convex, becoming gibbous, with a 

 shallow often scarcely defined sinuosity in the middle : hinge- 

 line slightly rising towards the beak, which is not incurved ; 

 area narrow, but distinctly defined : foramen broad, and show- 

 ing a narrow process which rises as high as the plane of the 

 area. Ventral valve much elevated towards the beak ; the 

 sides somewhat flattened, and the middle sometimes a little 

 depressed towards the front ; the beak slightly arcuate, and 

 the wide area nearly flat and moderately inclined backwards : 

 foramen large, and extending to the apex. 



Surface marked by twenty to twenty-four simple, strongly 

 rounded, slightly arching primary striae, which, by intercala- 

 tions of secondary striag, are often increased to twice that 

 number on the margin. 



Often the strise are simple throughout, and, when well pre- 

 served, are always marked by fine thread-like concentric striae, 

 and towards the margin by a few lamellge of growth. 



This species, in general form, resembles 0. plicatella ; but the area is 

 much larger, and extends to the salient cardinal extremities; while in 



[Assembly, No. 136.] 12 



