FOSSILS OF THE HUDSON EIVER GROUP. 105 



resemblance, both in size and general form, but the characters of the 

 sulci will serve to distinguish them, as well as the rounded, disc-like 

 character of the eye tubercle in the latter species. 



Formation and locality : In the shaly matter, between thin- bedded layers of lime- 

 stones of the Hudson Elver group, near Wayuesville, Ohio. 



Beyeichia quadeilirata (n. sp.). 



Plate 4, figs. 6, 7. 

 Carapace minute, the larger individuals seldom exceeding three- 

 hundredths of an inch in length, and often not more than that size. 

 Form sub-quadrangular, longer than wide, the proportions being about 

 as two to three, and a little the widest at the anterior third of the 

 length. Dorsal margin straight, a little less than the greatest length of 

 the valve; ends squarely rounded, and the basal line scarcely flattened. 

 General surface of the valves flattened, but marked by transverse fur- 

 rows, four in number, three of which are distinct and deep, extending 

 across, or nearly across, the valve ; the fourth is less distinctly marked' 

 and extends but little more than half way across the valve. The fur- 

 rows divide the surface of the valves into transverse ridges, which are 

 situated, one at each end, and one at each third of tlie length. Those 

 situated at the ends are narrow and abruptly elevated; that at the an- 

 terior third of the length does not reach quite to the dorsal margin; 

 while that of the posterior third is much the strongest, rapidly widens 

 in the lower part, and divided along the middle by the fourth, or smaller 

 furrow, which gives it the character of a strong ridge, bifurcating in the 

 lower half. The central furrow is wider than the others, oblique in its 

 direction, and somewhat curved in its course toward the ventral border. 

 The margin of the valves is strongly and abruptly depressed below the 

 general surface, forming a narrow, flange-like projection around the ends 

 and basal portions. Surface of the crust not spinose or granulose under 

 a lens of moderate power. 



The species somewhat resembles B. trisulcata, Hall, from the Lower 

 Helderberg group, in the general expression of the valves, but differs in 

 the relative position of the furrows. The specimens vary considerably 

 in the strength of the ridges, these, in some cases, being broad and 

 rounded, as in the specimen figured, while in others they are sharp and 

 narrow, leaving broader furrows between. 



Formation and locality: In the shaly matter, between thin layers of limestone of 

 the Hudson River group, near Waynesville, Ohio. Associated with Beyrichia Cham- 

 hersi and Isochilina cylindrica, and I. minutissima, Hall. 



