CONCHIFEEA, 



191 



oblong ; right valve with a curved, conic tooth in front of the 

 oblique, sub-trigonal cartilage-pit. Animal with thick united 

 siphons, fringed at the end, anal valve conspicuous ; foot finger- 

 like, with a byssal groove. Distrihution, 2 species. Britain, 

 France. Burrowing in oyster-shells and limestone, in 10 — 25 

 fathoms. Fossil, 20 species. Tertiary. Europe. 



Ne^ra, Gray. 



Etymology, Necera, a Eoman lady's name. 



Type, N. cuspidata, PI. XXIII., Fig. 5. 



Synonym, Cuspidaria, Nardo. 



Shell globular, attenuated, and gaping behind ; right valve a 

 little the smallest ; umbones strengthened internally by a rib 

 on the posterior side ; cartilage process spatulate, in each valve 

 (furnished with a movable ossicle, — Deshayes), with an obsolete 

 tooth in front, and a posterior lateral tooth ; pallial sinus very 

 shallow. 



Animal with the mantle closed ; foot lanceolate ; siphons short, 

 united, branchial largest, anal with a membranous valve, both 

 with a few long, lateral cirri. 



Distribution, 22 species. Norway, Britain, Mediterranean, 

 Canaries, Madeira, China, Moluccas, New Guinea, Chili. From 

 12—200 fathoms. 



Fossil, 14 species. Oolite — . Britain, Belgium, Italy. 



Fig. 266. Thetis, minor, Shy. Neocomian, I. Wight. 



Thetis, Sowerby. 



Etymology, Thetis, in Greek mythology, a sea-nymph. 



Synonyms, Poromya (anatinoides), Forbes. Embla (Korenii), 

 Loven ? Inoceramus (impressus), D'Orb ? Corbula (gigantea), 

 Sby. 



Type, T. minor, Fig. 266. T. hyaUna, PL XXIL, Fig. 11. 



Shell sub-orbicular, ventricose, thin, translucent, surface 

 regularly granulated, interior slightly nacreous; ligament (/) 



