120 
PALAEONTOLOGY OF NEW-YORK 
159. 6. ORTHIS PERVETA. 
Pl. XXXII. Figs. 5 a, b, c. 
Orthis perveta. 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 striae, 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 with several well known Trenton species at Mineral Point (Wisconsin). 
The associated species more particularly are the Orthis tricenaria , 0. pedinella, 0. tes- 
tudinaria , Leptcena sericea , Delthyris lynx , fyc. 
160. 7. ORTHIS iEQUIVALVIS ( n. sp .). 
Pl. XXXTI. 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 cost®, which are usually bifid or trifid, are marked as if by the bases of 
short spires, or of squamose 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 vieiv of the same, showing the equality of the valves. 
Position and locality. In Trenton limestone, Middleville? Cincinnati* 
