8 OLIVIDiE. 



Shell subovate ; aperture ovate ; pillar slightly thickened ; front 

 belt single, moderate. 8. Agaronia. 



III. Head hidden ; tentacles none ; eyes none. Foot short, very 

 broad, rounded on the sides, one-coloured. Operculum distinct. 



Spire conical ; sutural groove open to the apex ; aperture of 

 shell moderate ; operculum distinct ; foot very short, front 

 lobes linear. 9. Olivina. 



Spire conical ; sutural groove open to the apex ; aperture of 

 shell wide ; pillar lip thick, smooth, with two grooves in 

 front ; operculum none ? ; foot large, front lobes very large, 

 rounded. 10. Scaphula. 



Spire callous; sutural groove only open on the last whorls; 

 aperture moderate ; opercidum distinct. 11. Micana. 



I. Head exposed ; tentacles elongate, subulate ; eyes distinct, sub- 

 basal. Foot elongate, dilated, front lobes semicirctdar. 

 Operculum none. Shell with the front belt narrow. 



* Spire simple, with sutural groove open to the tip. 



Genus 1. STREPHONA. 



Shell subcylindrical ; spire conical or flattish, small ; aperture 

 linear ; pillar lip simple, only expanded in front, and not cover- 

 ing the callus ; front belt narrow ; inner lip cross grooved. Foot 

 elongate, longer than the shell, broad, rounded behind, dilated 

 on the sides, which are bent up and cover the shell ; the front 

 lobes nearly semicircular, rather produced, and acute at the 

 hinder outer angles. Head exposed ; tentacles elongate ; eyes 

 one-third from the base. Operculum none. 



Adanson, in his 'Hist. Nat. du Senegal,' regards all the 

 specimens of this genus as belonging to one species, observing : 

 — " La couleur de cette coquille est peu constante. J'en ai de 

 blanches, de jaunes, de j amies livids, de j amies verd, & meme 

 de verdatres sans aucun melange. J'en ai aussi qui, sur ces 

 differens fonds, sont tache"es, tigre"es, maibrees ou couvertes de 

 zigzags, qui s'elendent tantot sur leur longueur, tantot sur leur 

 largeur. Ces taches, ces points, ces bandes, et ces lignes sont 

 cendr6"s, noir ou bleuatre dans les lines ; brun, rougeatres ou 

 pourpres dans les autres : enfin leur melange est si vane", que ce 

 seroit perdre son terns que de faire l'e'nume'ration de toutes 

 celles qui ont ele" d^crites ou hgure'es par leurs auteurs. Je me 

 suis contente" de citer une vingtaine des principales variele\s aux- 

 quelles on peut rapporter toutes les autres, dont plus de deux cent 



