52 LEPAS. 



debted to a learned German conchologist,M. Schroter, is 

 about an inch high, and an inch and a half broad at the 

 base. It has six raised and six • depressed compart- 

 ments ; the former are very rugged, and resemble the 

 rough bark of a tree ; they are violet at top and greenish 

 towards the base: the latter are of a more uniform 

 violet colour, shining, and striated transversely. The 

 opening is nearly triangular; and the operculum, 

 according to Schroter, is composed of four valves, the 

 two anterior of which are striated obliquely. The base 

 of the shell is singular ; it is formed of a series of 

 striated laminae with serrated edges. These laminae are 

 irregular; the outer edge is flexuous, and the general 

 appearance of the base is not unlike a Madrepore. 



This shell was found by Mr. Sowerby, fixed to the 

 bottom of a vessel in the Thames. It has several small 

 specimens of the L. porcata on its sides, which were 

 purposely omitted in the plate. Fig. 3. and 4. repre- 

 sent the same shell in a young state, in which, without 

 particular attention, it may be mistaken for a distinct 

 species. Favanne has figured a young shell. The 

 French have copied Schroter. 



RIDGED ACORN. 

 PL 8. /. 5. Mr. Sowerby. 



23. Lepas porcata. L. testa conica, longitudinaliter porcata, violacea, 



apertura subovata. 

 Shell conic, ridged longitudinally, of a violet colour, with a somewhat 



oval mouth. 



This shell has six unequal valves, strongly ridged 

 longitudinally. The colour is violet, much deeper in 

 the furrows than on the ridges. Ridges, in the spe- 



