94 TRANSACTIONS OF THE WAGNER FREE 



the left valve) with a profound arciform ligamental furrow, and two nearly 

 horizontally placed cardinal teeth, separated by a broad, slightly curved, 

 dental sulcus ; muscular impressions sharply defined, deep ; external sur- 

 face rugose, covered with the somewhat sinuous lines of growth ; basal 

 margin entire, not crenulated. 



Length of largest specimen, measured along the antero-posterior axis, 

 and through the umbones, 3.7 inches ; height, nearly three inches ; depth 

 of a single valve somewhat over two inches. 



Common in the banks below Fort Thompson. 



This form may be readily distinguished from all the other species of 

 North American Chama, either recent or fossil, by its ponderous form, and 

 the near equality of the two valves, differing in the latter character con- 

 spicuously from the European Chama gryphoidcs, which much resembles 

 it. It differs in this respect also from the American Chama corticosa of 

 Conrad (Miocene), which, however, is a sinistral shell. 



Lucina disciformis, nov. sp. Fig. 28. 



Shell compressed, suborbicular, higher than broad, flattened on the 

 umbonal slope; beak subcentral, acute, overlooking a deeply impressed 

 lunule; ligamental sulcus profound; cartilage-pit oblique ; cardinal teeth 

 two in each valve, the posterior in the right valve, and the anterior in the 

 left valve, bifid ; anterior margin of shell impressed somewhat above the 

 middle ; muscular impressions elevated, the anterior ribbon-form, long 

 and narrow, departing somewhat from the rather distantly separated 

 pallial line; external surface ornamented with numerous distantly placed 

 lines of growth, which at nearly equal intervals rise into rugose elevated 

 lamella? ; interior of shell longitudinally rugated. 



Height, 2.5 inches ; width, 2.4 inches. 



This shell bears a similarity of outline to the Miocene Lucina Ameri- 

 cana (L. anodontd), and is barely distinguishable from that species by 

 external characters alone ; the latter is, however, edentulous. Among 

 recent forms it approximates L. Childreni, but that species is inequivalve. 



Area scalarina, nov. sp. Fig. 29. 



Shell obliquely rhomboidal, elevated, ventricose, angulated posteriorly, 

 flattened ; anterior end short, everjy rounded ; beaks prominent, trans- 

 verse, about eight, distant; ligament-area diamond-shaped, nearly smooth 

 in the young shell, with delicate transverse lines in the adult, with a 

 limited number of coarse, sinuous longitudinal lines ; hinge-line straight, 

 somewhat more than one-half the greatest length of shell ; teeth num- 

 erous, somewhat oblique toward either end. 



Ribs prominent, about twenty-four, broad, square, robustly crenate, 

 those of the left valve broader than the interspaces, flattened posteriorly, 

 about eight on the anal angulation ; those of the right valve of about the 



