FOSSILS OF THE NIAGARA GROUP. ^11 



There is a central longitudinal callosity extending from the apex 

 sometimes for one-third of the length of the muscular impression. 



The Stropliomena niagarensis of Winchell & Marcy (loc. cit.), appears 

 to me to be identical with this. The specimens in my possession, from 

 western localities, show a considerable variety of form and proportions, 

 and yet preserving the essential character of the species. 



A specimen communicated by Prof Winchell under the name S. 

 niagarensis, has the divaricator scars proportionally a little more elongate 

 than usual, but the same feature is preserved in other specimens. 



The specimen figure 3 is of a young or medium size, preserving a part 

 of the exterior surface of the ventral valve on the lower margin, while 

 the other portion is the impression of the exterior of the dorsal valve. 

 Fig. 4 is the cast of the interior of the ventral valve. 



Formation and Locality. — In limestone of the Niagara age, at Racine, 

 Wisconsin ; Bridgeport, Illinois, and Waldron, Indiana. - 



GENUS SPIRIFERA. 

 Spirifera eudora. Hall. 



PLATE XIII, FIGS. 5, 7. 



Spirifer eudora, Hall. Rep. Progress Geol. Survey Wisconsin for 1860, p. 25. 1861. 

 S. eudora, Hall. Transactions of the Albany Institute, IV, p. 211. 1862. 



Shell of moderate size, transversely subovate, length and width as three 

 to four, valves extremely gibbous ; hinge-line less than the width of 

 the shell below ; cardinal extremities rounded ; area moderately high ; 

 foramen triangular, a little higher than wide ; marked by three to four 

 simple, strong, angular plications on each side of the mesial fold and 

 sinus. Dorsal valve regularly arcuate ; beak somewhat incurved ; 

 mesial fold of moderate width, flattened above and slightly depressed 

 in the lower part. Ventral valve most prominent near the umbo ; 

 beak strongly incurved over the area ; mesial sinus broad and deep. 



The minute surface markings, as shown in specimens from Waldron, 

 Indiana, are fine radiating strise, precisely like those of S. macrophura 

 of the Lower Helderberg group of New York. The specimens from Wis- 

 consin are all casts of the interior. 



This species bears some resemblance to S. macropleura, but it is pro- 

 portionally more gibbous, the front more rounded, the area higher, and 

 the plications not directed so obliquely outwards from the beak. 



Cab. Nat. 48 



