38 PROCEEDINGS OF THE ACADEMY OF 



very convex, but in most, the shape resembles that of the true Clupeoids. 

 Bands of teeth on the intermaxillary, maxillary, dentary, palatine and pterygoid 

 bones, and on the tongue, most of which are very small and almost impercep- 

 tible. 



The genus is represented by species in the rivers and seas of South America, 

 Asia and Africa. Those of South America have the abdomen very convex ; in 

 those of the Old World, it is much less so. 



Type. Pellona Orbignyana Val. 



b. Ventral fins absent. 



Genus XIX. Pristigaster Cuv. 



Syn. Pristigaster Cuv. Regne Animal, vol. ii. 



Pristigaster Val. Hist. Nat. des Poissons, vol. xx. p. 326. 



Body compressed, with the back slightly arched, and with the abdomen very 

 convex, and strongly serrated. Teeth present on the intermaxillary, maxillary, 

 dentary, palatine and pterygoid bones, as well as on the tongue. Dorsal fin 

 higher than long, situated on the anterior half of the back. Lateral line 

 straight. 



The genus as now restricted contains only the South American species, dis- 

 tinguished by the scarcely arched back and very convex belly. The Indian 

 species belong to another genus. 



Type. Pristigaster cayanus Cuv. 



Genus XX. Opisthopterus Gill. 



Syn."? Apterygia Gray, Illustrations of Indian Zoology. 



Pristigaster sp. Val., Hist, Nat. des Poissons, vol. xx. 



Body compressed with the nape saillient, and the back convex ; the abdomen 

 convex, and strongly serrated. Teeth present on the intermaxillary, maxillary, 

 dentary, palatine and pterygoid bones, and on the tongue. Dorsal fin low and 

 small, situated at the end of the second third of the back's length. 



Type. Opisthopterus tartoor Gill. 

 Syn. Pristigaster tartoor Val., Hist. Nat. des Poissons, vol. xx. p. 328. 



Descriptions of Twenty-five New Species of TJNI0NID2E from Georgia, 

 Alabama, Mississippi, Tennessee and Florida. 



BY ISAAC LEA. 



Unio fabacecs. Testa lrevi, oblonga, subquadrata, subinflata, postice sub- 

 biangulata, subaequilaterali ; valvulis crassiusculis, antice crassioribus ; nati- 

 bus prominulis; epidermide tenebroso-fusca, micante, obsolete radiata; denti- 

 bus cardinalibus parvis, erectis, acuminatis, crenulatis ; lateralibus eurtis, la- 

 mellatis subcurvisque ; margarita purpurascente, salmonis colore tincta et 

 valde iridescente. 



Hab. Oostanaula River, Georgia. Bishop Elliott. 



Unio irrasus. Testa, hevi, rotundo-trigona, inflata, postice obtuse angulata, 

 antice rotunda; valvulis snbcrassis, antice crassioribus; natibus subelevatis, 

 crassis; epidermide luteo-fusca, vel obsolete radiata vel eradiata; dentibus 

 cardinalibus crassis, elevatis, subcompressis crenulatisque; lateralibus eurtis, 

 crassis, obliquis rectisque ; margarita argentea et iridescente. 



Hab. Etowah River, Georgia. Rev. G. White. 



Unio OcmcloHjensts. Testa laevi, transversa, inflata, postice obtuse biangu- 

 lata, antice subtruncata, valde insequilaterali ; valvulis crassis, antice crassi- 

 oribus; natibus prominulis; epidermide tenebroso-fusca, eradiata, superne 

 micaute, inferne valde striaia; dentibus cardinalibus parviusculis, pyramidatis 



[Feb. 



