CONCHOLOGICAL WRITINGS. 25 



two eyes and no tentacula jutting out of the perforation. It would 

 therefore deviate from the cha^racter of the family ; it may, probably, 

 at a future period become the type of another ; but the shell is so 

 very similar to Orbicula that I unite them now, proposing however 

 for it a sub-family, under the name of Notremidia, which may 

 become the family name when other similar genera shall have been 

 detected. 



Description. — Notrema. Generic character, Fluviatile bivalve 

 shell, inequivalve ; upper valve larger, nearly round, perforated in 

 the middle, opening operculated : lower valve lateral very small 

 inequilateral. Body flat beneath, head in the centre above, retracti- 

 ble, jutting out through the perforation, with two lateral eyes, no 

 tentacula. The generic name means opening, in the hack, in Greek. 



Nolrema fissiirella. Specific character. Upper valve convex 

 with circular wrinkles, and oblique transverse furrows : lower valve 

 flat obovate and smooth ; shell fulvous brown, opening round, oper- 

 culum round, brown, and shining, head truncate* 



Ohs. It is found on the rocks of the bottom of the river Ohio, 

 from the falls to the mouth ; it is rare ; diameter about one inch ; 

 it holds on wrecks as the Patellas do, and might be mistaken for 

 one at first ; the operculum has a hinge, when the animal wants to 

 protrude the head, it opens it as a valve. This shell might, perhaps, 

 be deemed trivalve on that account. 



C. S. Rafinesque. 



[From "Journal de Physique, de Chimie, d'Histoire Naturelle, etc." 

 Tome LXXXVIII. Paris, June, 1819.] 



PRODROME 



De to nouveaax Genres d'Animaux decouverts dans I'interieur de& 

 Etats-Unis d'Amerique, durant I'annee 1818 ; 



Par C. S. rafinesque, 



Professeur de Botanique et d'Histoire naturelle dans ITJniversite de Lex- 

 ingtan en Kentucky. 



VI Classe. MOLLUSQUES. 

 [4231 

 24. Pleurocera. (Spiral.) Coquille ovale ou pyramidale, plu- 



sieurs tours en aplomb. Ouverture oblique oblongue, base prolon- 

 gee tordue, sommet aigu. Levre exterieure mince, I'interieure col- 

 l&e sur la columelle qui est lisse et tordue, sans omJ)ilic. Animal a 



