52 BIVALVES ARCA. 



Magellanica — Magellan. J amaicensis — Jamaica. 



Reticulata — Reticulated. Campechensis — Campeachy. 



Candida — White. Lata — Broad. 



Indica — Indian. Senegalensis — Senegal. 



D. — Margin crenate, beaks inflected. 

 Undata — Lettered. Nummaria — Coin. 



Pectunculus — Spotted. *Nucleus — Silvery. 



Pectinata — Comb. Rhomboidea — Rhomhoidal. 



♦Glycimeris — Orbicular. Marmorata — Marbled. 



Pilosa — Downy, Angulosa — Angular. 



Scapha — Boat. 



OSTREA. — Oyster and Scallop. 



Animal — a Tethys: Shell bivalve, generally with unequal 

 valves, and slightly eared; hinge without teeth, hut fur' 

 nished with an ovate hollow, and mostly lateral trans- 

 verse grooves. 



There are no less than one hundred and thirty-six spe- 

 cies in this genus, which present considerable variety in 

 beauty and form. 



The Ostreae may be divided into two classes : the first 

 comprises the innumerable varieties of escallops or scallop 

 shells; the second, and much the least numerous, includes 

 the species somewhat resembling the common oyster. — 

 The former division is, for the most part, composed of 

 very elegant specimens: their form is usually regular, and 

 their surface is adorned with elevated divergent ribs, in 

 number from five to forty, which proceed fiom the tip of 

 the beaks, to the extremity of the margins, and there ter- 



