211 



part of the foramen. Dorsal valve depressed from the 

 umbo to near the middle, becoming subgeniculate in front ; 

 area about half as wide as in the ventral valve. Both 

 areas are distinctly striate, and marked by crenulations 

 of the hinge. 



Surface of the upper and middle portions of the shell, 

 marked by strong, irregular, distant, rounded, elevated 

 striae ; near the front of the shell the striae become more 

 crowded by the intercalation of one or more between the 

 principal ones. Entire surface marked by fine concentric 

 striae. Interior surface of valves marked by thickly set 

 pustules. Substance of shell very thin. 



This species has some resemblance to Strophomena euglypha 

 (Dalman), but is much more extended on the hinge, the 

 length and breadth being as two to three ; while in that 

 species the proportions are nearly as three to four. This 

 shell has not the fine intermediate striae, nor the punctate 

 surface of that species. The form is comparatively rare, 

 but three or four specimens having been obtained in the 

 entire collection. 



GENUS SPIRIFER. 

 Spirifer eudora (Hall.) 

 Spirifer eudora (Hall.) Jlnnual Geol. Report of Wisconsin, 1861. 



This species was originally described from casts from the 

 limestone of Racine, Wisconsin. The casts show a higher 

 area than the entire specimen ; since the strongly incurved 

 beak of the ventral valve covers much of the area, giving 

 a much less distance between the beaks of the opposite 

 valve, than shown in the casts. The surface is marked by 

 fine radiating striae, which are precisely of the character 

 of those of Sp. macropleura of the Lower Helderberg group. 



The figure given by Rcemer of Sp. niagarensis var. 



