262 MANUAL OF THE MOLLUSCA. 



sub-orbicular, ventricose, very thick near the beaks; ligaraeutal area long, wide, 

 sub-internal ; byssal groove close to the umbo ; right valve with a large, blunt 

 hinge-tooth; adductor impression single, placed anteriorly; pallial line dotted. 



Pterinea (lasvis) Goldf. 1832. Shell thick, rather inequivalve, very 

 oblique and broadly winged ; beaks anterior ; sinus shallow ; hinge-area long, 

 straight, narrow, striated lengthwise ; anterior teeth few, radiating ; poste- 

 rior teeth laminar, elongated ; anterior (pedal) scar deep, posterior (addactor) 

 impression large, very eccentric. Fossil, 25 sp. L. Sil. — Carb. U. S. 

 Europe, Australia. Pteronites (angustatus) M'Coy, 1844, is thinner and has 

 the teeth, &c. less developed, 



J/<?KO^^>, Bronn, 1830. M. salinaria, Schl. Trias, TidMtm. Obliquely oval, 

 compressed, radiated ; anterior side short, rounded ; posterior slightly eared. 



Si/n. ? Ralobia (salinarum) Br. 1830. Trias, Hallstadt. Semi-oval, ra- 

 diated, compressed, with a shallow sinus in front , hinge-line long and straight. 



POSIDONCMYA, BrOUU. 



Syn. Posidonia, Br. 1828. (not Konig). Poseidon, Neptune. 

 Tt/pe, P. Becheri, PL XVI. fig. 22. 



Shell thin, equivalve, compressed, earless, concentrically fiirrowed ; 

 hinge-line short and straight, edentulous. 



Fossil, 50 sp. L. Silurian — Trias. U. S. Europe. 



? Ayiculo-pecten, M'Coy, 1852 



Ti/pe, Pecten granosus, Shy. Min. Con. t. 574. 



Shell inequivalve, sub-orbicular, eared ; hinge-areas flat, with several 

 long, narrow cartilage fuiTows, slightly oblique on each side of the umbones; 

 right valve with a deep and narrow byssal sinus beneath the anterior ear-; 

 adductor impression large, simple, sub-central ; pedal scar small and deep» 

 beneath the umbo. 



Fossil (see Pecten). L. Silui'iau — Carb. Spitzbergen — Australia. 



Geryillia, Defrance. 



Etym. Dedicated to M. Gerville, a French naturalist. « 



Ex. G. anceps, PL XVII. fig. 1. 



Shell like Avicula ; elongated : anterior ear smaU, posterior wing-like : 

 area long and flat, cartilage pits several, wide apart ; hinge-teeth obscure, 

 diverging posteriorly. 



Fossil, 30 sp. Carb. — Chalk. Europe. 



Sub-genus ? BaJcewellia, King. B. ceratophaga, Schl. Fossil, 5 sp. 

 Permian, Brit. Germany, Russia. Shell small, inequivalve, cartilage pits 

 2 — 5; hinge with anterior and posterior teeth; anterior muscular impres- 

 sion and pallial line distinct. 



Perka, Bruguiere. 

 Eiym, Perna, a shell-fish (resembling a gammon) Pliny. 



