ARCA ARK. 177 



the shore ; all are marine. The mollusk has 

 no external siphons, it has a kind of compressed 

 peduncle, terminated by tendinous filaments, 

 which are affixed to rocks. The shells of this 

 genus which have the teeth arranged in a curved 

 line, have been formed into a new genus called 

 Pectunculus; * their form is orbicular, and 

 they are not attached to rocks, 



ARCA 

 NOAH'S ARK. 



Specific Character. Shell oblong, roundish at 

 one end, elongated at the other, narrow, and 

 inclining to angular ; beaks lateral, remote from 

 each other, the apices incurved with a broad 

 smooth space between them ; teeth in a straight 

 line ; surface strongly striated longitudinally, 

 and crossed with transverse lines ; margins sinu- 

 ous and somewhat gaping , of a pale rufous 

 colour, with dark oblique bands ; the broad 

 flat space between the apices has a few distant 

 grooves radiating from the umbones ; length 

 about an inch, breadth two. 



This singular shell much resembles the hulk 

 of a ship ; the flattened area and areola may be 

 considered as the deck, the pointed end the prow, 

 the gibbous and rounded end the stern, and the 

 acute edge of the united margins has the appear-. 



* Plate IX. figure 5. f Plate IX. figure 6. 



N 



