C. E. Beecher — N. A. Species of Strophalosia. 243 



Descriptions of Species. 



Strophalosia radicans Wmchell, sp. (Plate IX, figures 14-17). 

 Shell broadly elliptical, or ovate, wider than long ; greatest 

 width near the middle. Ventral valve conforming to the sur- 

 face of attachment, except at the elevated and free edges, 

 which are usually furnished with from ten to twenty tubular 

 spines extending downwards and adhering to the object of 

 fixation ; hinge with two strongly developed, slightly oblique, 

 cardinal teeth ; cardinal muscular impressions small, separated 

 by a slight ridge or septum. Dorsal valve convex at the beak, 

 flat or concave below, marked by lamellose concentric lines of 

 growth, and by a row of oblique wrinkles along the cardinal 

 line ; interior with a conspicuous, narrow, and elongate bifid 

 cardinal process extending beyond the hinge, and with deep 

 dental sockets on each side ; adductor muscular scars well de- 

 fined ; septum only developed in the central portion of the 

 valve ; reniform impressions distinct, enclosing a comparatively 

 small and strongly pustulose area. 



A ventral valve has a width, excluding spines of 7'5 mm , 

 and a length of 5*5 mm . The dorsal valve, figure 16, measures 

 8 mm in width and 5 mm in length. 



When well preserved, the spines are very rugose, and have 

 much the appearance of a minute annelid tube, as represented 

 in figure 17. They often extend 4 mm beyond the edge of the 

 shell, but are not so numerous nor so elongate as in S. Keokuk. 



A small ventral valve, growing in a cavity in the epitheca 

 of a coral, is attached only by the beak, and by spines from the 

 cardinal margin. The remainder of the valve is free, and the 

 whole form is very convex, with the surface marked by irregu- 

 lar lamellose strise and by infrequent short spines, which 

 become stronger and more elongate near the surface of attach- 

 ment. 



Geological position, — Shales of the Hamilton group, on spe- 

 cimens of Acervularia Davidsoni E. and H., and Zaphrentis 

 Trover sensis Winchell, Little Traverse Bay, Michigan. Pre- 

 sented to Yale University Museum by Professor Alexander 

 Winchell. 



Strophalosia scintilla sp. nov. (Plate IX, 10-13). 



Shell minute, broadly ovate, widest across the middle. Dor- 

 sal valve convex at the beak, fiat or concave below ; beak in- 

 conspicuous ; interior with small adductor muscular scars ; pus- 

 tulose near the margins ; reniform impressions not defined in 

 the single interior of this valve observed. Ventral valve 

 cemented to foreign objects ; margin elevated and usually 

 furnished with a variable number of short procumbent slender 

 spines, not exceeding six in the specimens examined ; hinge a 



