xxxii SYNOPSIS OF GENERA. 



surface ; more or less undulated or ribbed parallel to the free margins ; and 

 articulating with each other by means (only) of an external cartilage. Anterior 

 adductor muscular impressions, in general, near the antero-ventral margin. Sinus 

 deep in some species, and shallow in others." 



" Type, Hiatella sulcata, Fleming." 



In the volume of Plates and Explanations (1883), the name Sphenomya was 

 proposed as a sub-genus of Grammysia, differing from that genus in its ovate- 

 cuneate, oblique form, and absence of ligamental groove. It closely resembles 

 the typical form of Cuneamya, but also differs in the absence of the ligamental 

 groove. The name is at present confined to a single species. 



Example: Grammysia (Sphenomya) cuneata, pi. Ixii, figs. 1-9 ; xciii, fig. 19. 



Euthydesma, n. g. [Type, Astarte subtextilis, Hall.] 



Shell equivalve (?), inequilateral, broadly sub-ovate with a sub-alate cardinal 

 expansion. Cardinal line rigidly straight. Anterior end short. Beaks sub- 

 anterior. 



Surface marked by concentric striae of growth, and in the species described, 

 by slender radiating striae. 



Hinge-line straight, and marked by a distinct, continuous ligamental groove. 



But one species of this genus is at present known and its characters do not 

 seem to ally it with any described form. 



Example: Euthydesma subtextile, pi. Ixiii, figs. 11-16; xciii, figs. 28, 29. 



Edmondia, de Koninck (Anim. Foss. Carb. Belgique, p. 66). 1844. 



Shell equivalve, oval or sub-circular. Beaks varying from sub-central to 

 nearly anterior. 



Surface marked by concentric striae, and sometimes by obscure radii or fine 

 radiating striae. 



Hinge narrow, without teeth. Ligament external, contained in a groove 

 along the cardinal line. Muscular impressions not strongly impressed. Pallial 

 line simple. 



Examples: Edmondia Philipi, pi. Ixiv, figs. 9, 11-14, 17, 29; pi. xcv, figs. 1-4. 

 Edmondia subovata, pi. Ixiv, figs. 18-20, 26-28 ; pl. xcv, figs. 9-12, 



