XXX11 
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. lxii, 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. lxiii, 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. lxiv, figs. 9, 11-14,17, 29; pi. xcv, figs. 1-4. 
Edmondia subovata, pi. lxiv, figs. 18-20, 26-28; pi. xcv, figs. 9-12. 
