140 CORBULIDJE. 



rowing in oyster-shells and limestone, in 10-25 fathoms. Fossil, 

 20 sp. Tertiary; Europe. S. Binghami,Tnrton (cv, 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 digitiformbyssiferous 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. 



Etym. — Passing into the genus Mya. 



Syn. — Eucharis, Recluz, 1850. Embla, Loven, 1846. Cumingia 

 parthenopoea, Tiberi. ? Basterotia, Maj^er, 



Distr. — 10 sp. Britain, Scandinavia, Mediterranean, Tropical 

 America. Fossil, 13 sp. Cretaceous, Eocene ; France, Grer- 

 many, England, United States. P. granulata^ Nyst. (cv, 97). 

 P. quadrata, Hinds (cvi, 26). 



Animal with unequal siphons, clothed with numerous filaments, 

 foot narrow and slender. 



Shell suborbicular, subequivalve, and inequilateral, thin, 

 transparent, slightl}^ 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, Homes, 1859. 



Distr. — PL Mayeri, Homes (cv, 98, 99). Tertiary ; Europe. 



Shell oblong or quadrangular, equivalve, closed on both sides, 

 one large cardinal tooth in each valve, and a long groove 

 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, LyCCtt. 



Distr. — C. curtamsata^I'hU. Jurassic; England. 



" Shell equivalve, thin, inflated, posteriorly attenuated and 

 gaping, anteriorl^^ rounded, hinge with a small, depressed sub- 

 conical tooth in each valve, and extended, slightl}^ 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 Nesera, 

 but the tooth in each valve would recall Eucharis. Whether the 

 anterior laminar process occurs in both valves and whether it is 



