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 in- 

 clining 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 sinuous 

 and somewhat gaping, of a pale rufous colour, 

 with dark oblique bands ; the broad flat space 

 between the apices has a few distant grooves ra- 

 diating 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. t Plate IX. figure 6. 



N 



