PLAGIOSTOMA. CONCHIFERA. 81 



white, yellow, rose-coloured and purple, to shades and mixtures of these colours in 

 endless variegations. It is dredged for sale. 



P. variusj Lam. Shell ovate, with about thirty narrow elevated ribs 

 armed with vaulted spines, and the interstices transversely wrin- 

 kled ; auricles very unequal ; colour extremely variable, as in the 

 preceding. 2 inches long. Inhabits European seas. B Penn. 

 Brit. Zool. iv. pi. 64. 



P. sinuosus, Lam. Shell ovate, scabrous, irregularly tumid, with 

 about forty-five unequal filiform ribs, and the auricles unequal. 

 14 inch long. European coasts. B. Penn. Brit. iv. pi. 64, fig. 2. 



Gen. 19. PLAGIOSTOMA, Lam. 



Shell subauriculated, with the base transverse, straight ; beaks 

 slightly separate ; hinge without teeth ; depression for the 

 ligament conical, in part internal. 



The species of this genus are all fossil. In Britain they are found in lias, chalk, 

 and oolite. Fleming, Brit. Animals^ 388. 



Gen. 20. LIMA, Lam. Ostrea, Lin. 



Shell longitudinal, subequivalve, eared ; beaks separate, inclin- 

 ed outwards ; ligament external ; hinge without teeth. 



The shells of this genus are all marine, and almost always white. Fossil species 

 are found in France and Italy, and in Britain in oolite and lias. 



L. squamosa, Lam. (0. lima, Lin.) Shell oval, with about twen- 

 ty-two broad inuricated ribs with vaulted scales, and flattish on 

 one side ; hinge oblique. 2 inches long. Inhabits American 

 seas. D'Argenv. pi. 24, fig. E. 



L. glacialis, Lam. Shell oval, depressed, convex, nearly equilate- 

 ral, with numerous slender filiform scaly ribs ; margin entire ; 

 colour brownish white. 2J inches long. Inhabits American seas. 

 Lister, pi. 176, fig. 13. 



Gen. 21. PEDUM. Ostrea, Lin. 



Shell inequivalve, slightly eared, the lower valve tumid ; beaks 

 unequal, separate ; hinge without teeth ; ligament in part 

 exterior, inserted in an elongated furrow in the internal wall 

 of the beaks ; lower valve notched near the posterior base. 



P. spondyloideum, Lam. Shell ovate, wedge-shaped, depressed, the 

 upper valve striated longitudinally, and rough with granulations ; 

 colour white, slightly tinged with purple near the beak. 2^ in- 

 ches long. Indian seas. Very rare. Favanne, pi. 80, fig. K. 



SECTION III. 

 Ligament marginal, elongated. 



This section includes three families, Malleacea^ Mytllacea^ and Tridacnites. 



FAMILY I. MALLEACEA. 



Ligament marginal, sublinear, interrupted by crenulations or 

 simple ; shell foliaceous, more or less inequivalve. 



VOL. II. F 



