NIAGARA GROUP. 
105 
4. Strophomena transversalis. (Leptcena transversalis, Dalm. 1. c. p. 109, t. 1, f. 4 ; 
His. Pet. Suec. p. 69. t. xx, f. 5. Murchison, Silurian Researches, p. 629. pi. 13, f. 2.) — 
Semi-circular, lower valve very convex, upper one very concave, finely striated, and marked 
with linear distant, elevated ribs; “ hinge inflected; hinge line straight, equal in width to 
the width of the shell.” Our specimens are smaller than the figure of Murchison, and less 
prominently ribbed. Locality —Rochester ; Wayne county, and more rarely at Lockport. 
36. 
1. Delthyris Niagarensis, 4 and 4 a. Delthyris decemplicata. 7. a. b. c. Orthis hybriila. 
2 and 2 b. D. radiatus. 5. Orthis Flabellulum (a) 1 8. Delthyris sinuatus. 
3 and 3 b. D. staminea. 6 Orthis canalis. 
1. Delthyris Niagarensis. (Conrad Jour. Acad. Nat. Sci. p. 261.) — Semi-oval; ven- 
tricose in the middle, (but generally flattened from compression); ribs about twenty-two, 
rounded, not usually more than ten distinct on each side of the mesial fold, which on the 
upper valve is prominent, rounded, and expanding towards the base; whole shell covered 
with fine radiating striae, and usually a more prominent line in each depression between the 
ribs, the mark of which is sometimes left in the cast; hinge line shorter than the greatest 
width of the shell, rounded at the extremities. Width of the shell, one and a half inches ; 
length about one inch, but variable from compression. 
This fossil is peculiarly typical of the group, and will be readily recognized by its rounded 
ribs and finely striated surface, differing from all others of the genus in this part of the 
system. 
Locality— Lockport, Niagara, Rochester, and less abundantly in Wayne county. 
Geol. 4th Dist. 14 
