322 T. E. SAVAGE ALEXANDRIAN ROCKS OF ILLINOIS AND WISCONSIN 



Remarks : This variety differs from V. barrandei in the broader con- 

 vexity of the ventral valve from side to side, in the less sharp and promi- 

 nent mesial fold, in the less distinct sinus in the dorsal valve, in the better 

 defined radiating plications, and the larger size. 



Horizon and localities: Upper part of the Mayville limestone; near 

 Mayville, Brillion, and west of Sturgeon Bay, Wisconsin. 



Yirgiana barrandei var. major n. var. 

 Plate 17, Figures 1 and 2 



Description : Shell broadly ovate in outline, with the greatest width in 

 the anterior portion; the front margin rounded. 



Ventral valve arcuate from beak to front, highest posterior to the 

 middle, the curvature becoming progressively more convex posteriorly; 

 transverse convexity very strong; the postero-lateral margins abruptly 

 incurved, anterior margin less strongly convex; mesial fold in the casts 

 extending from near the beak to the front, very high and prominent, 

 especially in the middle and anterior portions; the beak is strongly ele- 

 vated and incurved; spondylium large, supported by a strong median 

 septum. 



Dorsal valve much less convex than the ventral ; highest posterior to 

 the middle, where the longitudinal and transverse convexity is moderately 

 strong ; the curvature is gentle over the anterior portion, where the valve 

 is frequently flat or concave; mesial sinus present only in the anterior 

 portion, where it is broad, shallow, and poorly defined; beak moderately 

 prominent ; crural processes making strong impressions in the casts. Sur- 

 face of both valves marked by numerous striae, which divide two or three 

 times between the beaks and the margins. The dimensions of a large 

 specimen are : length, 2^4 inches ; width, 214 inches, and thickness, 1% 

 inches. 



Remarks : Compared with V. barrandei var. mayvillensis, this form is 

 much larger and broader, with much stronger mesial fold in the ventral 

 valve and less distinct sinus on the dorsal, and weaker and more numerous 

 radiating striae. 



Horizon and locality : Upper part of the Mayville limestone ; at Marble- 

 head, Wisconsin. 



GENUS EURYPTERUS DE KAY 



Eurypterus pumilus n. sp. 

 Plate 17, Figure 8 



The ventral portion only is exposed in the type specimen of the above 

 species. The shell is so thin and the test has been so flattened by pressure 



