FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. V9 



the cardinal borders ; in the middle part of the valve is a mesial depression, 

 which extends from beak to base, and increases in depth and width only mod- 

 erately towards the front ; the umbo is inflated, and the beak elevated, pointed 

 and only slightly arched. 



Dorsal valve moderately convex only at the umbo, balance only slightly 

 curved, almost flat ; middle of valve is elevated from beak to front, forming a 

 well defined, but narrow and little elevated mesial fold, at the base of which 

 the front- margin is slightly sinuate. 



The surface is ornamented by simple sub-angular radiating striae, of which 

 four to five on each side of the mesial fold and sinus are more prominent, and 

 reach from the baso-lateral margins back to the beak ; they are, however, only 

 faintly marked in the umbonal region of each valve ; above these principal ribs 

 there are about four short ones on each side of the mesial fold and sinus, ter- 

 minating in the cardinal margins, the uppermost not more than about a line 

 from the dorsal beak. The illustration does not show this peculiar feature, 

 except in the side-view, where it is faintly indicated. These radii are crossed 

 by concentric lamellose, imbricating striae, which become crowded towards the 

 front, and which produce the rugose appearance of the shell. The specimen 

 before me measures six lines in width, four in length, and three in depth. 

 There are no plications on the fold nor in the sinus. This species is easily 

 distinguished from all other Rhynchonella. 



Formation and Locality. Found in the upper strata of the Niagara group, in the quarries east ot 

 the city of Louisville. It is of rare occurrence. 



Rhynchonella saffordi. HALL. 



Plate XXVII., figures 22. 23 and 24, and Plate XXXIII., figures 4, 5 and 6. 

 Rhynchonella saffordi, Hall. Can. Nat. and Geo., Vol. V., .Niag. group 1860. 

 Rhynchonella saffordi, Hall. 27th Kep. N. Y. State Mus., pi. 9, figs. 27-291875. 



Shell somewhat below medium size, varying from ovate to spherical, sub-pen- 

 tagonal, having the five sides almost equal, the front or base generally a little 

 larger than the lateral margins and the slopes of the beak ; shell very gibbous. 

 Ventral valve convex or depressed-convex, greatest convexity a little below 

 the umbo, from where it curves gently towards the lateral margins, but before 

 reaching these, it deflects very abruptly, almost forming here a right-angle ; 

 beak small and little arched, and slightly elevated above the one of the other 

 valve ; umbo scarcely noticeable. In the upper part of the valve, from apex 

 to one-third of its length, there is a slight elevation in the middle ; from the 

 point where this elevation ceases, some of the central plications become de- 

 pressed, which depression is only very slight but increases towards the front ; 

 here the depressed part of the valve makes a sudden and abrupt, almost angu- 



