MONOGRAPH OF THE GENUS 

 NAVICELLA. 



Fam. Neritacese. 



Char. Gen. Molluscum Traclielipodum fluviatile. Testa ellip- 

 tica^ superne couvexa, epidermide cornea induta, apice prope mar- 

 ginem posticum incurvo ; subtiis coiicava, labio interno septi- 

 formi. Operculum solidum, planum, radiatum, unidentatum. 



A genus of Trachelipodous fluviatile mollusks, with the shell 

 of an oval form, convex above, covered with a smooth epidermis, 

 with the apex simple and placed at or near the posterior margin ; 

 concave beneath, with a laminated, septiform inner lip. Oper- 

 culum shelly, rather quadrate, flat, radiating, and with generally 

 a sharp tooth-like process at the side. 



1. Navicella porcellana (pi. cxvii. f. 1, 2. pi. cxviii. Us. 

 i. 43, 44). Patella porcellana, Linn. Syst. Nat. p. 1257. Nerita 

 porcellana, Chemn. Conch, t. ix. p. 68. pi. 124. f. 1082. Patella 

 Borbonica, Vincent. Septaria Borbonica, Ferussac. Crepidula 

 Borbonica, De Boissi/. Navicella Perousii (N. elliptica, Quoy et 

 Gaimard), Recluz. NaviceUa elliptica, Lamarck, Soiverhy, ^r. 



N. testa ovali, valide convexa, sub epidermide varie nigro fas- 

 ciata vel reticidata ; apice recto, marginem paululmn superante ; 

 labio interno subangustato, margine recto ; operculo subquadrato, 

 brevi. 



Of the typical oval form, variously marked with black under a 

 transparent epidermis, very convex, with the apex nearly straight, 

 and slightly going beyond the margin. The septum is rather narrow, 

 with the edge nearly straight, and the operculum is of a rather 

 square form. 



The Bourbon Isles, the Mauritius, and Madagascar. 



2. Navicella macrocephala (pi. cxvii. f. 4, 5), Ze Guillon, 

 Rev. Zool. 1841, p. 374. 



N. testa subelongata, depressa, sub epidermide nigro divarica- 



4 b 



