262 MANUAL OF THE MOLLUSCA. 



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

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

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



Pterinea (Isevis) 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 (adductor) 

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

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

 the teeth, &c. less developed/ 



Monotis, Bronn, 1830, M. salinaria, Schl. Trias, Hallein. Obliquely oval, 

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



Syn. ? Halobia (salinarum) Br. 1830. Trias, Hallstadt. Semi-oval, ra- 

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



POSIDONOMYA, Bronn. 



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

 Type, P. Becheri, PL XVI. fig. 22. 

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

 hinge-line short and straight, edentulous. 



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



? AVICULO-PECTEN, M'Coy, 1852 



Type, Pecten granosus, Sby. Min. Con. t. 574. 



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

 long, narrow cartilage furrows, 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. Silurian Carb. Spitzbergen Australia. 



GERVILLIA, Defrance. 



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



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



Shell like Avicula ; elongated: anterior ear small, 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 ? Bakewellia, 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. 



PERN A, Bruguiere. 

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



