632 GEOLOGY OF OHIO. 



separated. Despile these and other differences, I wish it to be under- 

 stood that I think it just possible that B. grandis is not distinct from the 

 species intended by Mr. Miller. I tried to see his types but failed because 

 they were packed away. I am therefore obliged to rely upon his illus- 

 trations and to assume that they are correct. Comparing my specimens 

 with his figures it will be noticed that in the convexity of the valves and 

 the number of costae the two species agree very, well, but in all other 

 respects they are so obviously different that we are forced to regard them 

 as specifically distinct. The carinate umbones will distinguish the species 

 from all the other forms of the genus. 



There remains to mention that the outline of the shell and the coarse 

 rays, which however are rounded instead of flattened, remind of Anomal- 

 odonta gigantea, Miller. That species, however, is not so ventricose, and 

 is without the large depressed area which surrounds the byssal opening 

 in B. grandis. 



Formation and locality: Upper beds of the Cincinnati group, Ox- 

 ford and Clarksville, Ohio. 



Byssonychia cultrata, n, sp. 



Plate 45, Figs. 5-7. 



Size and outline practically the same as in B. grandis, while another 

 resemblance to that species is found in the carinate umbones. Critically 

 compared however a number of well marked differences will be observed. 

 First, the convexity of the valves is less, the thickness of an example 

 70 mm. high being only 30 mm. Second, the radiating costae are more 

 numerous, their number varying two or three either way from fifty-five. 

 Third, the upper part of the anterior side is almdst flat and not, as in that 

 species, deeply sunken about the byssal opening. Fourth, the posterior 

 lateral teeth are much stronger. And fifth, the ligamental area is much 

 narrower in a dorsal view, thus permitting the beaks to come into close 

 proximity. The ligamental area, in which the species differs also from 

 all the other species of the genus, consists of a narrow but deep and sharply 

 defined groove extending about two-thirds of the hinge from the beaks' 



Compared with other species B. robusla, Miller, will be found to be 

 more convex, relatively higher, and much straighter anteriorly, while most 

 of the remaining forms are readily separated by their rounded instead of 

 carinate umbones. 



Formation and locality : Upper beds of the Cincinnati group, Waynes- 

 ville, Ohio. 



Byssonychia richmondensis, n. sp. 



Plate 45, Figs 3 and 4. 



Ambonychia robusta (part), Miller, 1880, Jour. Cin. Soc. Nat. Hist., vol. Ill, p. 

 315. 



Shell large, high, triangular in a cardinal view, the anterior side be- 

 ing flat; .height, length and thickness of an average specimen, respectively, 



