370 TWENTIETH REPORT ON THE STATE CABINET. 



SPIRIFERA EUDORA. 



PLATE 13 (4), FIGS. 5 & 7. 



'^pirifer eudora : Hall, Geol. Report of Wisconsin, p. 25. 1861. 



" " " Transactions of the Albany Institute, Vol. 4. 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 ; fora- 

 men 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 strige, precisely like those of S. macropleura. 



The specimens from Wisconsin are all casts of the interior. 



This species bears some resemblance to <S. macropleura of the Lower 



Helderberg group of New-York ; but it is proportionally more gibbous, 



the front more rounded, the area higher, and the plications not directed so 



obliquely outwards from the beak. 



Formation and locality. In limestone of the age of the Niagara group, 



Racine, Wisconsin, and also in rocks of the same age at Waldron, Indiana. 



SPIRIFERA aiBBOSA. 



PLATE 13 (4), FIGS. 6 & 8. 

 Spirifer gibbosus .- Hall, Geol. Report of Wisconsin, page 25. 1861. 



Shell somewhat below the medium size, gibbous ; beaks slightly incurved, 

 area less than the width of the shell below, about three times as wide 

 as high ; cardinal extremities rounded; foramen large, higher than wide ; 

 valves marked by about four simple low rounded plications on each side 

 of the mesial elevation. Dorsal valve extremely gibbous on the umbo, 

 regularly arcuate transversely ; mesial elevation broad, flattened above ; 

 plications not extending to the beak, which is a little incurved. Ventral 

 valve deeper than the dorsal, but less arcuate ; mesial depression broad 

 and deep, rounded at bottom. Surface of both valves (in well preserved 

 specimens) show evidence of fine radiating striae. 

 This species resembles S. crispus of the Niagara group in New- York, 



but is much larger, frequently more than twice as wide as that species ; 



the mesial elevation is wider and not so high. The specimens described 



are all internal casts, so that the external surface characters cannot be 



fully given. 



Formation and locality. In limestone of the age of the Niagara group, 



Bacine, Wisconsin. 



