ANOMIID&. 293 
Shell suborbicular, very variable, translucent, and slightly 
pearly within, attached by a plug passing through a hole or 
notch in the right valve; upper valve convex, smooth, lamellar 
or striated; interior with a submarginal cartilage-pit, and four 
muscular impressions, three subcentral, and one in front of the 
cartilage ; lower valve concave, with a deep, rounded notch in 
front of the cartilage- -process ; disk with a single (adductor) 
impression. 
Animal with the mantle open, its margins with a short double 
fringe ; lips membranous, elongated; palpi fixed, striated on both 
sides ; gills two on each side, united posteriorly, the outer laminze 
incomplete and free; foot small, cylindrical, subsidiary to a 
lamellar and more or less calcified byssal plug, attached to the 
upper valve by three muscles; adductor muscle behind the 
byssal muscles, small, composed of two elements; sexes dis- 
tinct; ovary extending into the substance of the lower mantle- 
lobe. 
‘“There is no relationship of affinity between Anomia and 
Terebratula, but only a resemblance through formal analogy ; 
the parts which seem identical are not homologous.”—ForBEs. 
The Anomie are found attached to oysters and other shells, 
and frequently acquire the form of the surfaces with which their 
growing margins are in contact. 
paTRoO, Gray, 1849. Shell suborbicular ; two upper scars small, 
the lower one large. A. elyros, Gray (exxxiilli, 25). 
#NIGMA, Koch, 1845. Shell oblong, transverse. &. xnig- 
matica, Chemn. (¢xxxi,75). Lives attached to trees in mangrove- 
swamps. 
LIMANOMIA (Grayana), Bouchard. Fossil, 4 sp. Devonian; 
Boulogne. Inequivalve, valves thin near the beaks, slightly 
radially ribbed ; lower valve with a trigonal cut under the ear 
and near the beak. 
PLACUNOPSIS, Morr. and Lycett, 1853. Suborbicular, generally 
somewhat irregular, inequivalve ; larger valve convex, with small 
submarginal, submedian beak, and mostly ornamented with 
radiating ribs or strive; smaller valve flat, free, or attached to 
foreign objects; hinge toothless, with a small cartilage-pit in 
each valve ; muscular scar large, subelliptical, subcentral. Type, 
P. Jurensis, Roem. All the species as yet known are from 
Jurassic deposits, but it is not certain whether all the Jurassic 
species referred to Placunopsis agree with the characteristics 
above noticed; many of them appear to belong to Anomia 
(typical), and doubts are expressed on this point even regarding 
the type species, P. Jurensis. 
PracunAnoMIA, Broderip, 1832. 
Distr.—13 sp. West Indies, Britain, New Zealand, California, 
