LAS^A. 219 



the littoral zone, where they congregate in vast num- 

 bers, at the roots of small seaweeds, as well as in the 

 crevices of rocks and in the empty shells of Balani. On 

 some coasts they live as much out of the sea as in it, 

 a sufficient supply of water being retained within the 

 close-fitting valves to keep the gills moist until the 

 return of the tide ; and in many cases they must fast for 

 a long time, because they are found in places which are 

 covered by the sea at high springs only. A little fresh- 

 water bivalve (Pisidium pusillum) is also occasionally 

 amphibious. We have but one species of Lasaa, and 

 that is viviparous. Other species, however, have been 

 noticed in various parts of the world : 



" ..... Pr'ythee, think 

 There 's livers out of Britain." 



1. LAS^A RU'BRA*, Montagu.^ ^. 3? 



Cardium rubrum, Mont. Test. Brit. p. 83, tab. 27. f. 4. Kellia rubra, 

 F. & H. ii. p. 94, pi. xxxvi. f. 5-7 (as Poronia rubra), and (animal) 

 pi. O. f. 3. 



BODY white : mantle having its margin apparently plain and 

 without tentacles : eoccurrent tube sessile and concealed within 

 the mantle : foot broad at the base, the extremity being rather 

 rounded than pointed ; its bluish-white and transparent hue 

 is variegated by a line of dull but intense flake-white, which 

 runs from one end to the other. 



SHELL oval, with often a circular or triangular and rather 

 oblique outline, ventricose, not very thin or glossy : sculpture, 

 distant lines of growth and close-set wavy concentric striae, 

 besides more numerous but much finer longitudinal stria3, 

 which are so excessively minute as only to be seen with a 

 powerful lens : colour milk-white, tinged more or less deeply 

 with purplish-red, especially towards the hinge : epidermis 

 yellowish, rather thick : margins somewhat truncate and 

 rounded at the smaller or posterior end, slightly curved in 

 front, with sometimes a byssal sinus or indentation in the 



* Red. 



L2 



