ARC A ARK. 173 



of the species attach themselves to rocks by a 

 kind of byssus : these have always the shell 

 more or less gaping ; but the greater part of the 

 Arks live buried in the sand at a short distance 

 from the shore ; all are marine. The mollusca 

 have no external siphons, they have a kind of 

 compressed foot, terminated by tendinous fila- 

 ments, which are affixed to rocks. 



ARCA NO<B.* 



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 darker 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 

 appearance of the keel. The form of the shell 



* Plate IX. figure 6. 



15* 



