MULTIVALVES. — LEPAS. 29 



of the animal; which, through their medium, performs 

 those functions that are necessary to its existence. 



The Lepas is never found independent or isolated, as 

 most other shells are ; on the contrary, all its species are 

 known to attach themselves in clusters, by their base or 

 fleshy stalk, to other bodies, as rocks, coral reefs, and shells; 

 even fish themselves are not exempt from their encroach- 

 ments ; the whale, for instance, is frequently found with 

 groups of Lepades adhering to various parts of its body. 

 They also affix themselves to ships, and, though at first in- 

 visible, so rapid is their increase in magnitude and num- 

 ber, that the velocity of a vessel is considerably impeded by 

 them. I once observed, on the coast of Africa, a piece of 

 wood, which had been placed as a buoy, in a few days be- 

 come covered with a gelatinous substance, and in less than 

 a fortnight was thickly beset with Lepades. Hence it would 

 appear, that the animal exists in the sea in the state of ani- 

 malcule. 



The exterior of the shell is often varied in form, cover- 

 ing, and colouring; the usual outline is conical; in some, 

 it resembles a pyramid, and in a few is parabolical, or even 

 hemispherical; the Lepas diadema partakes of the latter 

 form and bears some resemblance to a divided globe. 



The number of valves which constitute the shell is very 

 indefinite ; their usual amount is six, but the Lepas palmi- 

 pes has sometimes only four; and other species possess 

 the intermediate gradations of number, as far as twenty- 

 four, which number is sometimes exceeded in the L. poUi- 

 cipes. The valves are variously diversified with stri*, 

 ridges, and grooves. 



The ridges are mostly longitudinal ; the striae, on the con- 

 trary, are transverse, and not unfrequently beset with rough 

 projections and acute spines, as is the case in the Lepas 

 spinosa. 



