30 PANDORID^. 



usual hyaline protrusile valve; this tube is speckled with 

 minute sand-like ])oints ; each tube is encircled at its base by 

 a lew cylindrical filaments, which are somewhat longer than 

 the tubes, and are occasionally speckled with flake-whito : 

 gills and palps pale brown : foot flexible, white, cloven at the 

 heel, whence byssal filaments are produced. 



Shell irregularly rhomboidal, the left or convex valve some- 

 what overlapping the other, of a membranous consistency, 

 opaque and lustreless : scalptLire, numerous rows of fine gra- 

 nulated stria), radiating from the beaks to the outer margins ; 

 between each of these stritc are five or six rows of minute 

 and close-set tubercles or pores, which are connected with tlie 

 tubular structure of the external layer of the shell ; there are 

 also occasional lines of growth : colour pale yellowish-white : 

 epidermis light-brown, and having an agglutinating property, 

 by means of which the surface becomes invested with a coat 

 of sand and Foraminifera or other organic remains : mar<iins 

 broad and rounded on the anterior side, flexuous or somewhat 

 indented in front, curved obliquely upwards to the posterior 

 side, which is prolonged into a beak-like form and truncated 

 at that end, with a double but indistinct ridge in the left 

 valve, and a corresponding furrow in the right ; dorsal margin 

 incurved : healcs triangailar, inclining to the anterior side ; 

 umbones rather prominent : cartilatje golden-yellow, lying 

 nearly parallel with the hinge-lino, and contained in a groove 

 in each valve, the sides of which are thickened : himje-line 

 obtusely angular: him/e-jjlate long, strengthened by a rib in 

 the left valve, which fits into a slight furrow in the opposite 

 valve : ossicle irregularly quadrangular, with the broader end 

 towards the posterior side, where it is notched or forked ; the 

 narrower end is truncated and placed immediately under the 

 beaks : inside highly polished and iridescent ; edges thin, re- 

 flected or folded outwards in the right valve : muscidar scars 

 often double. L. 0-875. B. 1-7. 



Var. elonqata. Shell more slender, and transversely elon- 

 gated : Osteodesma elonqata, (Gray) Hanley, llec. Sh. p. 25, 



pi. 13. f. 27. J '^ ^) y^ 



Habitat : All our coasts, in sand, from 4 to 86 f., 

 but nowhere common. The variety has been found in 

 the Hebrides and Shetland. L. Norveyica has not been 

 noticed as a British fossil ; but Philippi has recorded it 



