44 I.EPAS. 



cipal essential characters, being nuiltivalve, imd 

 parasitical ; and the species pass gradually from 

 one conformation to the other in so connected a 

 series, that it would seem needless, and indeed de- 

 structive of simplicity and order, to separate or dis- 

 arrange them. The aperture in the conical divi- 

 sion increases propojrtionably to the growth of the 

 shell, by means of the extension, in width, of the 

 triangular parts between the valves. The pedun- 

 cled species are called Barnacles, from a strange 

 prejudice formerly entertained', that they were 

 transformed into geese ; originating perhaps in 

 their feathery tentacula, and in their being 

 observed moving about on their long flexible tubes 

 above the surface of the water. Both divisions are 

 invariably attached to extraneous substances, 

 usually in groups. 



The genus takes its name either from Xv-rag, the 

 rock, to which the shells adhere, or from Xirrag, the 

 denomination bestowed by the ancients on the 

 family of Patellse, on account, probably, of the 

 5ca/e-like manner in which they are adherent. 



