58 THE ELEMENTS 



vessel when the valves are united. 

 Many of the Arks are, however, void 

 of this character, but are sufficiently 

 united to the genus, by the number 

 and construction of their teeth. 



The French Conchologists have 

 made two genera of the Area: Area 

 and Nuclia. The Area Noae is an 

 example of the former, and the Area 

 Nucleus of the latter. 



In Turton^s Linne forty-two species 

 are described ; and six species have 

 been found on the British shores. 



Genus 14th.-OSTREA, (or oyster.) 

 Animal 'dTeihys : shell bivalve, gene- 

 rally with unequal valves, and slightly 

 eared ; hinge without teeth, but fur- 

 nished with an ovate hollow, and 

 mostly lateral transverse grooves. 

 Linn. Syst. 313. Plate 7th, fig. 14th. 



The Ostrea is divided into three 

 families : *valves radiated and eared, 

 as in scallops ; **rugged or rough, as 

 in the oyster ; ***hinge with a perpen- 



