458 MANUAL OF THE MOLLUSCA. 
DIPLODONTA, Bronn. 
Etymology, diplos, twin, odonta, teetn. 
Synonym, Spheerella, Conrad. 
Type, D. lupinus (Venus) Brocchi. Pl. XITX., Fig. 9. 
Shell sub-orbicular, smooth; ligament double, rather long, 
sub-marginal; hinge-teeth 2.2, of which the anterior in the 
left valve, and posterior in the right, are bifid; muscular im- 
pressions polished, anterior elongated. 
Animal with the mantle-margins nearly plain, united; pedal 
opening large, ventral; foot pointed, hollow; palpi large, free 
gills two on each side, distinct, the outer oval, inner broadest 
in front, united behind; branchial orifice small, simple; anal 
larger, with a plain valve. 
Distribution, 40 species. West Indies, Rio, Britain, Medi- 
terranean, Red Sea, West Africa, India, Corea, Australia, Cali- 
fornia. D. diaphana (Felania, Recluz) burrows in sand. 
Fossil, 30 species, Eocene —. United States, Europe. 
? Scacchia, Philippi, 1844; Tellina elliptica, Sc. Shell minute, 
ovate, posterior side shortest ; hinge-teeth 1 or 2, laterals obso- 
lete; ligament minute; cartilage internal, in an oblong pit. 
Animal with mantle widely open; siphonal orifice single ; foot 
compressed, linguiform; palpi moderate, oblong. Distribution, 
2 species. Mediterranean. fossil, 1 species. Pliocene, Sicily. 
? Cyamium, Philippi, 1845. CC. Antarcticum, Pl. XIX., 
Fig. 16. Shell oblong; hinge-teeth, 2.2; ligament double; 
cartilage in a triangular groove behind the teeth in each valve. 
Distribution, 3 species. Patagonia, Northern Europe. Jossil, 
1 species. Tertiary, Hurope. 
UNGULINA, Daudin. 
Etymology, ungulina, like a hoof. 
Type, U. Oblonga. Pl. XIX., Fig. 10. 
Shell sub-orbicular; ligament very short; epidermis thick, 
wrinkled, sometimes black; hinge-teeth 2.2; muscular im- 
pressions long, rugose. 
Animal with the mantle open below, fringed ; siphonal orifice 
single; foot vermi-form, thickened at the end and perforated, 
projecting from the base of the shell or folded up between the 
sills, palpi pointed; gills two on each side, unequal, the 
external narrower, with a free dorsal border, inner widest in 
front. 
Distribution, 4 species. Senegal, Philippines, oxcayating 
winding galleries in coral. 
