198 CHAMID^. 



Animal with the mantle closed ; pedal and siphonal orifices 

 small, snbequal ; foot veiy small ; gills two on each side, very 

 unequal, united posteriorly. 



Chama (Pliu}^), 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. G. 

 lazarus, Linn, (cxvi, 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 (cxvii,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 laj^er is laminated by oblique lines of growth, with corru- 

 gations at right-angles to the laminae ; 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 indiflerently by either valve ; when 

 fixed by the right valve the dentition is reversed, the left valve 

 having the single tooth. 



ARCINELLA, Schumacher, 181T. 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 Chamte are very irregular in form and sculp- 

 ture; the same species may be simply ribbed, or foliated, or 

 spinose, according to circumstances. The consequence of this 

 variability has been an undue multiplication of species. 



MoNOPLEURA, Matheron, 1842. 

 Distr. — Fossil, 10 sp. Neocomian — Chalk; France, Texas. 

 M. Urgonensis, Matheron (cxvii, 2). 



