TRIGONIA, Bnujuiere. 



Thes. pi. 492, 



Testa sequivalvis subtrigona, intus vivide iridescente 

 margaritacea, rosea argentea vel aurea ; extus radiatim 

 nodoso-costata, purpurea, vel rosea vel alba, epidermide tenui 

 fusco induta, Cardo dentibus in valva dextra duobus divari- 

 catis oblique serratis, in valva sinistra duobus duplicatis, 

 divaricatis et serratis. Ligamentum externum. 



The two single serrated diverging teeth fittiug into two 

 double ones, and the pearly lining of the interior impart a 

 singular beauty to the shells of TrigonitE ; the former re- 

 minding one a little of the Unio tribe generally, and the 

 latter of Castalia in particular-. They are, however, marine, 

 and have strong radiating nodose ribs. 



(Species. 



1. Lamarckii, f, 1-4, Gray. — Ovato-subtrigona, purpurea, 

 purpureo fasciata, vel aurantia ; costis approximatis, dense 

 mouiliferis radiata ; latere postico declivi, anguste truncato, — 

 The smaller of the two best known species and more closely 

 ribbed than the others. 



2. UNIOPHGRA, f. 9, 10, Gray. — Brevis subquadi'ata ; pur- 

 pureo fasciata vel alba ; costis distantibus, subdistanter 

 nodosis, ad aream pusticam magis approximatis ; area postica 

 subquadrata, late truncata. — Shorter from anterior to pos- 

 terior side tlian T. Lamarckii, with the ribs more distant, 

 and the posterior area more broad and square. 



3. MARGARITACEA, f. 6, 7, Lamurck. — Oblique subovata 

 snbcompressa alta roseo-purpurea vel alba ; distanter nodoso- 



