258 ARCID A. 
MEGAMBONIA, Hall, 1859. Shell ventricose, broad-ovate or 
suborbicular; anterior end with a ventricose wing or extension, 
separated from the body of the shell by a deep curved sinus; 
anterior hinge-teeth unknown; lateral teeth two to three, short, 
small and oblique; ligamental area narrow or obsolete ; anterior 
muscular scar deep, circular, and having a small pedal scar upon 
its upper margin; posterior scar larger, faintly impressed; pallial 
line simple. C. aviculoidea, Hall (cxxix, 9). 
ApRANARIA, Munier-Chalmas, 1876. 
Syn.—Siliquarea, Pseudarea, Tromelin and Lebese. 
Distr.—2 sp. Paleozoic; France. <A. T'romelini, M.-C. 
Shell equivalve, recalling Cultellus by its general form ; hinge 
with a series of oblique linear, nearly parallel teeth, the anterior 
ones narrower and more divergent, the posterior more numerous ; 
a rib within each valve passes in front of the anterior muscular 
impression. 
CarpioLA, Broderip, 1834. 
Distr.—17 sp. U. Sil.—Devon.; Eur., U.8. CC. cornucopiz, 
(exvi, 94). ’ 
Shell somewhat inequilateral or subequilateral, roundly ovate, 
with the beaks incurved anteriorly and with a rather large liga- 
mental area between both; hinge-line slightly curved with 
numerous oblique pliciform teeth, being apparently present on 
both sides of the beak; surface generally radiately striated or 
ribbed. 
LyRropEesMA, Conrad, 1841. 
Syn.—Actinodonta, Phil. 
Distr.—Fossil, 4 sp. Lower Silurian ; Canada, United States, 
Britain. ZL. pulchella, Hall (cxxvii, 83). 
Shell Trigonia-shaped, rather elongated, with a striated poste- 
rior area; hinge with several (5-9) radiating teeth, striated 
across; ligament external. 
Lyrodesma appears to connect the Pectunculus with the 
Arcine. 
Prcruncutus, Lam. 
Syn.—Axinea, Poli, 1791. Tuceta, Bolten. 
Distr.—58 sp. West Indies, Britain, India, New Zealand, 
West America; ranging from 8 to 60, rarely 120 fathoms. 
Fossil, 80 sp. Neocomian—; Europe, United States, South 
India, P. Delesserti, Reeve (cxxvii, 53). 
Shell orbicular, nearly equilateral, smooth or radiately striated ; 
umbones central, divided by a striated ligamental area; hinge 
with a semicircular row of transverse teeth; adductors sub- 
equal; pallial line simple; margins crenated inside. 
Animal with a large crescent-shaped foot, margins of the sole 
