120 PALEONTOLOGY OF NEW-YORK 



159. 6. ORTHIS PERVETA. 



Pi,. XXXII. Figs. 5 a, b, c. 

 Orthis pervcta. Conrad, Proc. Acad. Nat. Sci. Philadelphia, 1843, Vol. i. p. 333. 



Transversely suboval, somewhat wider below than the length of the hinge line ; valves 

 slightly ventricose, nearly equal ; surface marked by numerous fine radiating strioe, which 

 bifurcate on the umbo ; ventral valve with a slight almost imperceptible depression along 

 the middle ; dorsal valve with a broad elevation in front, producing a sinuous margin ; 

 cardinal area partially common to both valves, as likewise the deltoid foramen. 



Length about one third of an inch ; breadth nearly half an inch. 



Fig. 5 a. View of the ventral valve, and area of the dorsal valve. 

 Fig. 5 b. Cardinal view of the same specimen. 



Fig. 5 c. Profile view, showing the width of the area, and the projecting beaks on both valves. 

 Fig. 5 d. Cardinal view magnified, showing that the area and foramen are partially common to both 

 valves. 



I have adopted this species, with the three preceding ones, from Mr. Conrad, as they 

 occur associated witii several well known Trenton species at Mineral Point ( Wisconsin ) . 

 The associated species more particularly are the Orthis tricenaria, 0. pectinella, 0. tes- 

 tudinaria, Leptana sericea, Delthyris lynx, 8fc. 



160. 7. ORTHIS ^QUIVALVIS ( n. sp.) . 

 Pl. XXXII. Figs. 6 a, b, c. 



Subrotund ; valves almost equally convex ; length nearly equal to the breadth ; sides 

 contracted just below the cardinal line, which is less than the greatest width of the shell ; 

 area narrow ; foramen small ; dorsal valve differing from the ventral, in the beak being 

 slightly extended, and scarcely curved over the foramen ; surface marked by about twenty 

 rather sharp radii, with deep intermediate spaces ; radii strongly marked entirely to the 

 beak, and becoming bifid or trifid towards the middle of the shell. 



This species is easily recognized, from the almost perfectly equal valves, the beak of the 

 dorsal valve being only a little more extended than that of the ventral valve. The strong 

 radiating striae or costae, which are usually bifid or trifid, are marked as if by the bases of 

 short spires, or of squamosc projections of the shell, which, in perfect specimens, indicate 

 a character much like Atrypa aspera. 



Fig. 6 a. View of the ventral valve, showing the beak of the dorsal valve, a small portion of the area, 



and triangular foramen. 

 Fig. 6 b. View of the dorsal valve. 

 Fig. 6 c. Cardinal view of the same, showing the equality of the valves. 



Position and locality. In Trenton limestone, Middlcville? Cincinnati. 



