ADDENDA. 



Ortliis stroplioniciioides. 



Plate XXIII. Fro. 7 a, b, d,f, g. 



For explanation of these figures, which illustrate more completely the character 

 of the species, see explanation accompanying Plate xxiii, volume of plates. 



Oitliis cuiiiberlandia ( n. s.). 



Plate XCV A. Fig. 20 & 21, 



Shell large, suborbicular, depressed. Ventral valve depressed convex in 

 the middle and towards the beak, flattened or scarcely concave towards 

 the front : area narrow and short ; foramen large ; dental lamellae 

 thin ; muscular area broadly flabelliform. 



The surface externally marked by numerous fine sharp striae, which are 

 increased by interstitial additions. 



This species approaches the 0. tuhulostriata in many of its characteristics, but is 

 sufficiently distinct to be easily identified, the strise being finer and the beak less 

 prominent. It has the form of muscular impression common to 0. ohlata and others 

 while it is a thinner shell with more prominent striae. 



Fig. 20. The exterior of a ventral valve of this species. 



Fig. 21. The interior of a smaller ventral valve of the same. 



Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 

 f Pal^ontolooy III.] 61 



