6 MULTIVALVES LEPAS. 



and even hemispherical; the Lepas Diadema partakes of 

 the latter form, and somewhat resembles a divided globe, 

 The number of valves which constitute the shell is often 

 very indefinite, their usual amount is six ; but the Lepas 

 Palmipes has sometimes only four; and other species pos- 

 sess the intermediate gradations of number, as far as twen- 

 ty-four, which amount is not unfrequent in the Lepas 

 Pollicipes. — ^The valves, of whatever number they con- 

 sist, are variously diversified with striae, ribs, and 

 grooves. 



The ribs are mostly longitudinal ; the strice, on the 

 contrary, are transverse, and not unfrequently beset with 

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

 Lepas Spinosa, 



The color also differs considerably, though the most 

 usual complexion is of a blueish, purplish, or reddish 

 cast, intermixed with a whitish hue. However, some are 

 pied with black and green alternately, and others are of 

 a greyish- white, or dirty-yellow tint, as may be observed 

 in the Lepas Mitella, and others. 



The valves which compose the lid or operculum, often 

 vary in their number and shape ; sometimes they only 

 consist of two, at others, of three and four, and not unfre- 

 quently of a far greater number. — They are usually attach- 

 ed to a ligament, and sometimes present a pointed or 

 acute form, while in other species they are perfectly blunt 

 or obtuse. 



The interior of many of this genus, is a mere vacuum j 

 but in others it is either filled up with tubular pores, as 

 in the Lepas Porosa, or else is divided into separate com- 

 partments or chambers. 



Notwithstanding the great affinity which exists 

 throughout the Lepas tribe, yet there are a few excep- 



