VERTICOItDIA. 531 



Genus TRIGONIA, BriiQuiere. 



Shell equivalve, inequilateral, sub-trigonal ; surface of 

 valves externally longitudinally ribbed or furrowed ; inter- 

 nally iridescent and pearly. Hinge composed of two 

 oblong, divaricate, lamelliform teeth in the right valve 

 transversely grooved on both sides, and four in the left 

 valve grooved on one side only. Ligament external, thick, 

 marginal. 



Ex. T. margaritacea, Lamarck, pi. 124, fig. 1. Shell, 

 T. margaritacea, fig. I, a, 1, b. 



There are five species of recent Trigonim, from the 

 Australian seas. The animals are enabled to make con- 

 siderable leaps like the Cockles by means of their angulated 

 foot ; they abound in some parts of Sydney harbour. 

 Nearly one hundred extinct species have been discovered in 

 the Chalk and Trias of Europe, the United States, Chili, 

 the Cape, and Southern India. 



Species of Trigonia. 



Lamarckii, Gray. Strangei, A. Adams. 



margaritacea, Lam. uniophora, Gray. 



nobilis, A. Adams. 



Genus VERT1CORDIA, Searles Wood. 



Shell sub-orbicular ; surface of valves externally ra- 

 diately ribbed, and covered with a brown epidermis ; inter- 

 nally brilliantly pearly ; margins denticulated; beaks sub- 

 spiral. Hinge with two teeth in each valve ; right valve 

 with a long posterior tooth ; ligament internal, oblique. 

 Adductor scars two, faint ; pallial line simple. 



