494 MANUAL OF THE MOLLUSCA. 
Shell oblong, gaping at each end; posterior side shortest; 
ligament large and prominent; epidermis black, extending 
beyond the margins; anterior muscular scar long, pallial im- 
pression irregular, slightly sinuated. 
Animal larger than its shell, sub-cylindrical ; mantle closed, 
siphons united, protected by a thick envelope; orifices small ; 
Fig. 268. Glycimeris siliqgua, Chemn. Newfoundiand. 
a, a, adductor muscle; p, pedal muscle; s, siphonal muscle; f, foot; #, labial 
tentacles ; g, gills, much contracted and crumpled. 
pedal opening small anterior ; foot conical; palpi large, striated 
inside, the posterior border plain; gills large, extending into 
the branchial siphon. 
Distribution, 2 species. Arctic Seas, Cape Parry, North 
Western America, Newfoundland. : 
Fossil, Plocene—. Britain, Belgium. 
FAmMILy XJX.—ANATINIDA. 
Shell often inequiyalye, thin; interior nacreous; surface 
granular; ligament external, thin; cartilage internal, placed 
in corresponding pits and furnished with a free ossicle; 
muscular impressions faint, the anterior elongated; pallial 
line usually sinuated. 
Animal with mantle-margins united; siphons long, more or 
less united, fringed; gills single on each side, the outer lamina 
prolonged dorsally beyond the line of attachment. 
Pholadomya and its fossil allies have an external ligament 
only; has no ossicle. The external surface of these shells is 
often rough with large calcareous cells, sometimes ranged in 
lines, and covered by the epidermis; the outer layer consists of 
polygonal cells, more or less sharply defined; the inner layer is 
nacreous. 
