140 CORBULID A. 
rowing in oyster-shells and limestone, in 10-25 fathoms. Fossil, 
20 sp. Tertiary; Europe. §S. Binghami, Turton (ev, 96). 
Shell oblong; right valve with a curved, conic tooth in front 
of the oblique, subtrigonal cartilage-pit. 
Animal with long, thick, united siphons, fringed at the end, 
anal valve conspicuous; foot finger-like, with a byssal groove. 
The prolonged siphons and the short digitiform byssiferous foot 
fairly distinguish the animals of this genus from those of Corbula. 
The hinge is occasionally very similar in both. As a rule the 
teeth in Sphenia become obsolete with age. 
Poromya, Forbes, 1843. 
Ktym.— Passing into the genus Mya. 
Syn.—KEucharis; Recluz, 1850. Embla, Loven, 1846. Cumingia 
parthenopea, Tiberi. ? Basterotia, Mayer. 
Distr.—10 sp. Britain, Scandinavia, Mediterranean, Tropical 
America. Fossil, 13 sp. Cretaceous, Eocene; France, Ger- 
many, England, United States. P. granulata, Nyst. (ev, 97). 
P. quadrata, Hinds (evi, 26). 
Animal with unequal siphons, clothed with numerous filaments, 
foot narrow and slender. 
Shell suborbicular, subequivalve, and inequilateral, thin, 
transparent, slightly nacreous within; valves closed, surface 
granulated ; teeth, in right valve a short but strong cardinal, 
and in the left a minute triangular cardinal and a ridge- ‘like 
lateral on the posterior side. 
PLEURODESMA, Hornes, 1859. 
Disir.—Pl. Mayeri, Hornes' (ev, '98, 99). Tertiary ; Europe. 
Shell oblong or quadrangular, equivalve, closed on both sides, 
one large cardinal tooth in each valve, and a long aroove 
extending along the dorsal margin of the shell for the reception 
of the cartilage ; there is no indication of the presence of a liga- 
ment. This genus has been proposed for a tertiary shell, Pl. 
Mayeri, agreeing in general form with Eucharis, but differing 
widely in the form of the hinge. 
CorBURELLA, Lycett. 
Distr.—C. curtansata, Phil. Jurassic; England. 
“Shell equivalve, thin, inflated, posteriorly attenuated and 
gaping, anteriorly rounded, hinge with a small, depressed sub- 
conical tooth in each valve, and extended, slightly thickened, 
laminar plate forming a kind of an anterior lateral tooth or 
process.” Ligament and pallial sinus are not noticed, nor are 
they perceptible in the figure. In general form is near Neera, 
but the tooth in each valve would recall Eucharis. Whether the 
anterior laminar process occurs in both valves and whether it is 
