274 PAL.^OI^TOLOGY. 



half the width of the shell below, and isloi)ing somewhat rapidly from the 

 center to the extremities on each side of the beak. Left valve hicrhly con- 

 vex, becoming almost subangular on the umbone; auriculations subequal, 

 quite small and indistinctly separated from the body of the shell by very 

 slight, rounded depressions, extending from the beak to the margin on each 

 side, in which they cause slight sinuosities, the anterior one most distinct. 

 Beak small, somewhat pointed, and slightly projecting beyond the cardinal 

 line. Surface of the valve marked by fine, even, rounded, thread-like radi- 

 ating striae, scarcely visible without the aid of a lens; also by finer concen- 

 tric lines. Right valve not observed. 



The species presents much the appearance of many forms of Lima, and 

 it is possible it should be so referred ; but there is no other evidence of a 

 cardinal area on the left valve than the sloping of the hinge-line, while the 

 wings and sinuosities are more like those of Aviculopcdcn. 



We know of no species so closely related to this one as to be readily 

 mistaken. 



Formation and locaUty. — In limestone of the Upper Coal-Measures 

 (Permo-Carboniferous), foot-hills southeast of Salt Lake City, Wahsatch 

 Range, Uta'h. S. F. Emmons, collector. 



AVICULOPECTEN PARVULUS U. sp. 

 Pl.ate VI, tig. 6. 



Shell quite small, equilateral, broadly ovate in outline, a little higher 

 than wide; sides and base rounded, slightly prolonged on the postero-basal 

 side, and obscurely angular near the middle of the anterior margin. Hinge- 

 line two-thirds as long as the greatest width of the shell, longest on the 

 anterior side, and very moderately sloping from the beak. Left valve 

 highly convex; wings moderate, not distinctly separated from the body of 

 the shell; anterior one largest, the margins nearly rectangular to each other, 

 the sinus scarcely perceptible, forming oidy a broadly-curved indentation 

 below the angle; posterior wing small, the margins forming an obtuse 

 angle. Surface of the valve highly convex; beak small and olitusely 

 pointed, barely projecting beyond the cardinal line. Body of the valve 

 marked by alternating larger and smaller radii, the stronger ones extending 



