174 FISSURELLA. 



F. OMICRON Crosse & Fischer. PI. 22, figs. 45, 46, 47. 



Shell of an oval, depressed form, ornamented outside by radiat- 

 ing ribs, crossed by fine concentric strise, especially developed 

 toward the summit, and giving that part of the shell a granular 

 appearance. The intervals between the ribs are occupied by radiat- 

 ing striae. The inside is smooth, shining, bluish-white. Margin 

 simple, acute. Fissure oval, bordered within. (Fischer.) 



Length 13, breadth 10 mill. 



Saint Vincents Gulf, S. Australia. 



F. omicron C. & F., Journ. de Conchyl. 1864, p. 348 ; L c. 1865, 

 p. 41, t. 3, f. 4-6. 



Species of which the habitats are unknown. 



F. OLIVACEA Gray. PI. 59, figs. 51. 



Shell ovate, scarcely attenuated anteriorly, rather conical, 

 radiately somewhat irregularly roughly ridged, ridges obsoletely 

 nodose ; orifice oblong-ovate, slightly contracted in the middle ; 

 whitish, neatly rayed with olive. (five.) 



Habitat unknown. 



F. olivacea GRAY, SOWERBY'S Conchol. Illust., f. 57. EVE. Conch. 

 Icon., f. 61. 



F. BALANOIDES Eeeve. PI. 59, fig. 40. 



Shell ovate, a little attenuated anteriorly, rather conical, smooth, 

 radiately slightly grooved ; orifice oblong-ovate, a little contracted 

 in the middle ; yellowish, sometimes faintly tinged with rose, rayed 

 with olive and dark green, rays marked with lines of the color 

 darker, greenish white around the orifice. (Rve.) 



Habitat unknown. 



F. balanoides EVE. Conch. Icon., f. 66. SOWB. Thes., p. 192, f. 

 94. 



Compare F. nimbosa. 



F. MELVILLI Sowerby Jr. PI. 59, fig. 29. 



Shell oval, rather elevated, broad behind, slightly contracted in 

 front; radiately closely ribbed, ribs very little raised, alternately 

 larger ; concentrically wrinkled ; pale green, interior greyish-white. 



