159 



TRIGONIANA.— Two Genera. 



Trigonia. Shell equivalve, triangular, sometimes suborbicular; cardinal 

 teeth oblong, laterally compressed, diverging transversely, furrowed; two in 

 the right valve, furrowed on each side, and four in the other, furrowed only 

 on one side. Lig'ament external, marginal. 



T. pectinata, 15 fossil species. 



Castalia. Shell equivalve, inequilateral, triangular; the beaks eroded, 

 recurved posteriorly; hinge with two lamellar teeth, transversely striated; the 

 posterior one distant, shortened, subtrilamellar; the other anterior, elongated, 

 lateral. Ligament external. 



C. ambiefua. 



NAIADA.— Four Genera. 



Fresh water shells, the hinge of which is sometimes furnished icith an irreg- 

 ular, simple or divided cardinal teeth, and a longitudinal one, which extends 

 under the corselet, and sometimes no tooth, or is furnished with irregular, 

 granular tubercles, through its whole length. Muscular impression posterior, 

 compound; the beaks decorticated, often eroded. 



Unio. Shell transverse, equivalve, inequilateral, free; beaks decorticate, al- 

 most eroded; muscular impression posterior, compound; hinge with two teeth 

 in each valve; one cardinal, short, irregular, simple, or divided in two, substri- 

 ated; the other elongated, compressed, lateral, prolonged under the corselet. 



Ligament external. 



U. radiatus, 

 (Gmelin.) 



U. undulatus, 



U. complanatus, 

 (Solander,)hab. 

 rivers and lakes 

 E. of Alleghany 

 mountains. 



radiata. Virginiata, Lam. 

 radiatus, Barnes. 

 Say's Am. C. p. ii. f. 8. 



Say's Am. C. p. xvi. 



'purpureus. Say, Am. C. 

 pi. iii. f. 1. 



rarisulcata, Lamarck. 



coarctata, ' 



purpurascens, ' 

 { rhomb ula, ' 



georgina, ' 



sulcidens, ' 



Caroliniana, Bosc. 



fluviatilis, Green. 

 (, carinifera, Lamarck. 



U. ovatus, 

 (Say.) 



' ovata, Lamarck, 3 by 4 inches. 

 Say's Am. C. pi. ii. f. 7. 1st ed. 

 Hildreth in Sil. J. v. 14. f. 21. 



U. cariosus, fluteola, Lamarck. 

 (Say.) Sil- | cariosa, ' 



liman's J. { crassus, Say. (old.) 

 v. 6. pi. xi. | carinatus, Barnes, (rayed. 

 f. 10. a. b. l^ellipticus, ' (young. 



U. nasutus, ) 

 Say's A. C. I . , _ . 

 pi. iv. f. 1 f rostrata J valen. 

 1st ed. J 



