CONCHIFERA. 4093 
pearly within, attached by a plug passing through a hole or 
notch in the right valye: upper valve convex, smooth, lamellar 
or striated ; interior with a sub-marginal cartilage-pit, and 
four muscular impressions, 3 sub-central, and one in front of 
the cartilage (see Fig. 213, p. 402): 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 2 on each side, united posteriorly, the outer 
laminz 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. 
i A. pernoides, from California, there is an anterior (pedal) 
muscular impression in both valves. 
“There is no relationship of affinity bet eeen Anomia and. 
Terebratula, but only a resemblance through formal analogy; 
the parts which seem identical are not homologous.” (Forbes.) 
The Anomiz are found attached to oysters and other shells, 
and frequently acquire the form of the surfaces with which 
their growing margins are in contact. They are not edible. 
Distribution, 20 species. North America, Britain, Black Sea, 
India, Australia, West America, Icy sea. Low water — 100 
fathoms. 
Fossil, 36 species. Oolite —. Chili, United States, Europe, 
Tndia.: 
Sub-genera. Placunomia (Cumingii), Broderip. Synonym, 
Pododesmus, Phil. P. macroschisma, Pl. XVI., Fig. 4. Upper 
valye with only two muscular impressions; the pedal scar 
radiately striated; the byssal plug is often fixed in the lower 
valve, and its muscle becomes (functionally) an adductor. Dis- 
tribution, 13 species. West Indies, Britain (P. patelliformis), 
New Zealand, California, Behring’s Sea, Ochotsk. — 50 
fathoms. : 
Limanomia (Grayana), Bouchard. Shell eared like Zima. 
Fossil, 4 species. Deyonian; Boulonnais, China? 
PLacuna, Solander.—Window-Shell. 
Etymology, plakous, a thin cake. 
Example, P. sella, Pl. XVI., Fig. 5. 
Shell suborbicular, compressed, translucent, free, resting on 
T 
