198 CHAMIDA. 
Animal with the mantle closed; pedal and siphonal orifices 
small, subequal; foot very small; gills two on each side, very 
unequal, united posteriorly. 
CuaMaA (Pliny), Linn. 
Distr.—50 sp. Tropical seas, especially amongst coral reefs ; 
fifty fathoms. West Indies, Canaries, Mediterranean, India, 
China. Fossil, 40 sp. Cret.—; United States, Europe. C. 
lazarus, Linn. (exvi, 98). 
Shell attached usually by the left umbo ; valves foliaceous, the 
upper smallest ; hinge-tooth of free valve thick, curved, received 
between two teeth, in the other; adductor impressions large, 
oblong, the anterior encroaching on the hinge-tooth. 
Animal (exvii, 3,4) with the mantle-margins united by a cur- 
tain, with two rows of tentacular filaments; siphonal orifices 
wide apart, branchial slightly prominent, fringed, anal with a 
simple valve; foot bent, or heeled; liver occupying the umbo 
of the attached valve only; ovary extending into both mantle- 
lobes, as far as the pallial line; lips simple, palpi small and 
curled; gills deeply plaited, the outer pair much shorter and 
very narrow, furnished with a free dorsal border, and united 
behind to each other, and to the mantle; adductors each com- 
posed of two elements. 
The shell of Chama consists of three layers; the external, 
colored layer is laminated by oblique lines of growth, with corru- 
gations at right-angles to the laminz; the foliaceous spines 
contain reticulated tubuli; the middle layer is opaque white, and 
consists of ill-defined vertical prisms or corrugated structure ; 
the inner layer, which is translucent and membranous, is pene- 
trated by scattered vertical tubuli; the minute processes that 
occupy the tubuli give to the mantle (and to the casts of the 
shell) a granular appearance. 
Some Chamas are attached indifferently by either valve ; when 
fixed by the right valve the dentition is reversed, the left valve 
having the single tooth. 
ARCINELLA, Schumacher, 1817. Shell nearly regular and equi- 
valve, ribbed and spiny, with a distinct lunule, attached by the 
right valve. C. arcinella, Linn. (cxvi, 99). The subgenus is 
scarcely warranted by its distinctive characters. Like most 
attached shells, the Chame are very irregular in form and sculp- 
ture; the same species may be simply ribbed, or foliated, or 
spinose, according to cireumstances. The consequence of this 
variability has been an undue multiplication of species. 
Monopieura, Matheron, 1842. 
Distr.—Fossil, 10 sp. Neocomian—Chalk; France, Texas. 
M. Urgonensis, Matheron (exvii, 2). 
