Genus 3. 

 PHOLAS. 



GENERIC CHARACTER. 



Animal Ascidia. 



Testa bivalvis, divaricata, cum minoribus accessoriis diftbrmibus, ad 



cardinem. 

 Cardo recurvatus, cartilagine eonnexus. 



Animal an Ascidia. 



Shell, two-valved, divaricated, with smaller accessory valves of a dif- 

 ferent shape at the hinge. 

 Hinge folded back, connected by cartilage. 



GENERAL OBSERVATIONS. 



The species of this genus vary in the number of 

 their accessory valves, which are in all very fragile, and 

 so slightly connected to the shell, that we rarely find 

 them quite perfect. The two principal valves are, for 

 the most part, open at both ends, and their surface, 

 which is generally striated, is in some species as rough 

 as a file. The animal inhabiting this genus of shells 

 has a very thick membranous mantle, or sheath, open 

 at both ends. From the superior opening of this 

 mantle proceeds a double neck, or two united siphons, 

 one of which is larger than the other. These siphons 

 are slightly toothed on their edges, and serve, one for 

 the entrance, and the other for the exit of the food. The 

 animal has likewise a foot which is short and conic. 



The faculty which these soft animals possess of pene- 

 trating hard substances, such as stones and wood, has 



