12 INVERTEBRATA OF MASSACHUSETTS. 



from their parents. These float about in the sea in countless 

 numbers, until they come in contact with some substantial resi- 

 dence, to which they unceremoniously affix themselves, and then 

 assume the shape and habit of the parent. 



The obstruction they cause to vessels is the only material harm 

 they do ; while, on the other hand, they afford no little protec- 

 tion to wharves, the piles of bridges, and other submerged wood- 

 en structures, by encasing them with a bony crust. 



Only two or three species permanently inhabit our shores ; but 

 as they are constantly seen and collected at all our wharves and 

 ship-yards, I have thought proper to regard them as denizens. 



The C impedes are naturally divided into two groups ; those 

 which are sessile (sessilia), or seated firmly and directly upon 

 their station, and those which are mounted upon a stem or stalk 

 (pedunculata) . 



t SESS1LIA. Shells sessile. 

 GENUS CORONULA, LAM. 



Shell of jive consolidated pieces, conoid, truncated at its extrem- 

 ity ; walls very thick, interiorly excavated into radiating cells ; 

 operculum of four valves. 



Shells belonging to this genus live attached to the skin or shell 

 of some marine animal. Two or three species of them live, 

 partially imbedded, in the skin of the whale. This monster of 

 the deep is not unfrequently taken in the vicinity of Cape Cod and 

 Cape Ann, and one species of barnacle has been found upon him. 



CORONULA DIADE'MA. 



Shell globose-conical, truncated at tip ; surface exhibiting six 

 triangks, each of which has four ribs, marked across with beaded 

 striae. 



State Coll., No. 255. Soc. Cab., No. 2075. 



Lepas diactema, LIN., MONTAGU ; Test. Brit. 13. WOOD j Index, pi. 1, f. 2. BORN ; 

 Jtft.,t.l,f.5,6. GuAL T .;t.l06,f.A. Phil. Trans. 1758, t. 34, f. 1. CHEMN.J 

 C<mc/,,viii.t.99,f.843,844. LISTER ; Conch., t. 445, f. 288. DONOYAH 5 1M*. 

 Shells, ii. t. 56, f. 1, 2. 



