178 BIVALVES. 



ance of the keel. The form of the shell 

 suggested the name of Noah's Ark, and from 

 this fancied resemblance in one species to the 

 ark, the genus owes its designation. 



This shell is affixed to rocks by a very strong 

 tendinous substance, there is an open space in the 

 front of the valves, through which it issues. 



It inhabits the Mediterranean, Indian ocean, 

 West Indies, and Britain. 



ARCA Undata* 



LETTERED ARK. 



Specific Character. Shell suborbicular, nearly 

 smooth, with faint reticulated f striae ; margin 

 crenated ; teeth in a curved line ; colour white, 

 variegated with yellowish red spots, in undu- 

 lated transverse bands. 



Inhabits the West Indies, and shores of Italy. 

 It belongs to the modern genus Pectunculus. 



* Plate IX. figure 5. 



f Reticulated, having the appearance of net work, from 

 the latin reticulum, a small net. 



