304 CYPRINIDJE. 



latitude, which were submerged during a comparatively 

 recent geological period ; and they attest the extent of 

 its diffusion in the glacial epoch. Other species occur 

 in tertiary strata of an older formation ; and the history 

 of the genus, according to Mr. Searles Wood, may per- 

 haps date back from the Greensand. 



This genus was called Arctica by Schumacher, and 

 Cardia, Nympha, and Asmidia by other authors. 



Cyprina Islan'dica *, Linne. 



Venus Islandica, Linn. Syst. Nat. p. 1131. C. Islandica, F. & H. i. p. 441, 

 pi. xxix, and (animal) pi. M. f. 4. 



Body yellowish -white : mantle powdered for some depth 

 with minute red-brown sandy points ; margin thickened, and 

 marked with a slender brown line : tubes nearly sessile, tinged 

 with red-brown ; each orifice is encircled at the base of the 

 cirri which fringe it with a narrow bright red line, varying in 

 intensity of colour ; cirri simple, about 20 surrounding the 

 incurrent, and about half that number the excurrent tube ; 

 from the latter tube frequently protrudes a globular, trans- 

 parent, membranous valve : gills pale brown, unequal, coarsely 

 pectinated, the outer leaflets more triangular and smaller than 

 the inner : palps two on each side, pectinated, of moderate 

 length, triangular and pointed : foot thick at the stalk or ful- 

 crum, rather long and sharply pointed. 



Shell obliquely triangtdar, gibbous towards the beaks, 

 thick, rather glossy : sculpture, numerous fine laminar and 

 slightly undulating concentric striae, which become coarser and 

 more irregular at the sides : colour yellowish-white faintly 

 tinged with pink : epidermis chestnut passing into dark brown, 

 of a lighter cast or sometimes yellowish with a prismatic hue 

 in the young ; it is marked, like the surface of the shell, with 

 laminar strise : margins curved in front and at the anterior 

 si'ie, obliquely truncate at the lower posterior end, and on 

 that side bluntly angular, with an indistinct fold or flexure, 

 which is more observable in immature specimens : beaks con- 

 siderably recurved : ligament strong and raised, horncolour or 

 dark brown, partly enclosed in a groove on the dorsal edge : 

 hinge-line obtusely angular : hinge-plate thick, broad, and 



* Icelandic. 



