MACTRINJS. 375 



Shell. equivalve. Hinge with two cardinal teeth in each 

 valve, the hinder small, compressed, often rudimentary, the 

 front triangular, more or less deeply notched ; lateral teeth 

 of left valve simple, of right valve double ; cartilage in an 

 internal triangular pit behind the cardinal teeth. Siphonal 

 inflection distinct. 



Sub-fam. MACTRIN.E. 



Mantle-lobes free. 



Shell sub-triangular, ovate, nearly closed behind ; lateral 

 teeth distinct, well-developed, laminar. 



Genus TRIGONELLA, Da Costa. 



Shell trigonal. Hinge with the cardinal teeth moderate; 

 lateral teeth elongate, linear, sub-equal; ligament mar- 

 ginal, triangular, separated from the cartilage-pit by a 

 shelly ridge. Pallial sinus rounded. 



Ex. T. stultorum, Linnaus, pi. 99, fig. 1. Shell, T. 

 stultorum, fig. 1, a, 1, b. 



The species of Trigonella inhabit all seas, especially 

 those within the tropics. They principally affect the sandy 

 shores, where they live buried a little beneath the surface. 



Species of Trigonella. 



abbreviata, King. apicina, Desk. 



achatina, Chem. attenuata, Desk. 



Adansoni, Phil. contraria, Desk. 



alba, Lam. corallina, Linn. 



autiquata, Spengl. corbiculoides, Desk. 



Aphrodina, Desk. cordiformis, Desk. 



