Ambonychia (bellistriata), Hall, 1847. Nearly eq^uiyalve, 

 gibbose, oblique, obtusely -winged. A. vetusta (Inoceramus, 

 Sby.) is concentrically furrowed ; the right valve has a small 

 anterior ear (usually concealed) separated by a deep and narrow 

 sinus. Fossil) 12 species. Lower Silurian — Garb. United 

 States, Europe. 



? Cardiola (interrupta), Broderip, 1844. Equivalve, gibbose, 

 obliquely oval, radiately ribbed ; beaks prominent ; hinge-area 

 short and flat. Fossil, 17 species. Upper Silurian — Dev. 

 United States, Europe. 



? Eurydesma (cordata), Morris ; Devonian? New South Wales. 

 Shell equivalve, sub -orbicular, ventricose, very thick near the 

 beaks ; ligimental 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 (Isevis), Goldf. 1832. Shell thick, rather inequivalve, 

 very oblique and broadly winged ; beaks anterior; sinus shallow ; 

 hinge-area long, straight, narrow, striated lengthwise ; ante- 

 rior teeth few, radiating ; posterior teeth laminar, elongated ; 

 anterior (j)edal) scar deep, posterior (adductor) impression large, 

 very eccentric. Fossil, 32 species. Lower Silurian — Garb. 

 United States, Europe, Australia. Pteronites (angustatus) 

 M'Goy, 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. 



Synonym, P Halohia (salinarum) Br. 1830. Trias, Hallstadt. 

 Semi-oval, radiated, compressed, with a shallow sinus in front ; 

 hinge-line long and straight. 



PosiDOisroMTA, Bronn. 



Synonym, Posidonia, Br. 1838 (not Konig). Poseidon, Neptu-pe. 



Type, P. Becheri, PL XYL, Fig. 22. 



Shell thin, equivalve, compressed, earless, concentrically 

 furrowed ; hinge-line short and straight, edentulous. 



Fossil, 50 species. Lower Silurian — Trias. United States, 

 Europe. 



P Ayictjxo-I'Ectek, 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 

 s .nus beneath the anterior ear ; adductor impression large, 



T 3 



