CONCHIFERA. 



277 



leeply plaited, the outer pair much shorter and very narrow, furnished with a 

 'ree dorsal border, and united behind to each other, and to the mantle ; ad- 

 luctors each composed of two elements. 



Fig. 184. Right Side. Fig. 185. Leftside. 



Animal of Chama (from Torres Str. Mr. Jukes.) 

 Fig. 184. Right side, with the umbonal portion of the mantle removed. 

 Fig. 185. Leftside, showing the relative extent of the liver and ovarium. 



a, a, adductors; m, pallial line; e, excurrent orifice; 6, branchial; /, foot and 

 >edal orifice; p, posterior pedal muscle; t, palpi; g, gills (contracted); I, liver; o, 

 varium ; d, dental lobes. 



The shell of Chama, consists of three layers ; the external, coloured layer 

 5 laminated by oblique lines of growth, with corrugations at right angles to the 

 aminae ; the foliaceous spines contain reticulated tubuli : the middle layer is 

 paque white and consists of ill-defined vertical prisms or corrugated struc- 

 ture ; the inner layer, which is translucent and membranous, is penetrated 

 y scattered vertical tubuli; the minute processes that occupy the tubuli 

 ive to the mantle (and to the casts of the shell) a granular appearance (fig. 

 85, 1, m.) 



Some Chamas are attached indifferently by either valve ; when fixed by 

 he right valve the dentition is reversed, the left valve having the single 

 ooth. Chama arcinella, which is always attached by the right umbo, has 

 tie normal dentition 1:2; it is nearly regular and equivalve, and has a dis- 

 inct lunule. 



Distr. 50 sp. Tropical seas, especially amongst coral-reefs ; 50 fms. 

 V. Indies, Canaries, Medit. India, China. 



Fossil, 30 sp. Green-sand . U. States, Europe. 



Sub-genus ? Monopleura; Matheron (= Dipilidia, Math) M. imdri- 

 ata, Math. Fig. 187. Neocomian, S. France. Shell attached by the 

 'extral umbo ; valves alike in structure and sculpturing ; fixed valve straight, 

 aversely conical, with a long, straight ligamental groove, and obscure hinge- 

 rea; opercular valve fiat or convex, with an oblique, sub-marginal umbo. 



