OPEECULAE. 221 



" Oliviform ; spire (typically) rather produced ; the tip acute ; 

 inner lip not thickened ; outer lip straight ; base of the piUar 



. curved inwards, and marked by two strong plaits ; upper plaits 

 obsolete or wanting ; aperture effused at the base only ; biplicata. 

 Tank. Cat, 2332. purpurata. Zool. 111. ii. 58. f. 1. mutabilis. 

 Say. eburnea. Zool. 111. ii. 58, f. 2. conoidalis. Lam. No. 57. 

 oryza. Lam. No. 62." 



OLTG-TE,A. Say. " Helicina," Lamarck, was first applied by 

 Lamarck to Eotella, and afterwards to the genus of operculated 

 land shells, to which " Olygyra" should perhaps in strictness be 

 now given. 



OMALAXIS. Desh. Subsequently Bifeontia. Desh. Tig. 354. 



ONISCIA. Sow. (G. B.) Fam. Purpurifera, Lam. Entomos- 

 tomata, Bl. — Bescr. Oblong, sub-ovate, slightly turbinated, can- 

 cellated ; spire short ; aperture elongated ; terminating anteriorly 

 in a very short, recurved canal ; outer lip thickened, denticu- 

 lated within ; inner lip spread over a portion of the body whorl, 

 granulated. — Ohs. The granulated inner lip is the principal 

 character by which this genus is distinguished from Cassidaria. 



. In Oniscia the canal is not so produced. Mr. Eeeve's Monograph 

 contains 7 species. C. oniscus, PI. xviii. fig. 409. 



ONUSTUS. Humph. A genus proposed by Humphrey and 

 adopted by Swainson who describes it thus : " Shell trochiform, 

 the surface irregidar, and often covered with extraneous bodies, 



, cemented and incorporated Avith the calcareous substance of the 



. shell ; the under part of the body whorl flattened or concave, 

 umbilicate. O. Solaris. Mart. 173. f. 1700, 1701. Indicus. lb. 

 172. f. 1697. 1698." A thin lamina extending beyond the angle 

 of the body whorl from the outer lip gives a concavity to Phorus 

 Indicus, and is considered by some authors sufficient to distin- 

 guish it from the genus Phorus. 



ONYTHOCHITON. Gray. Chiton undulatus, and simHar 

 species. 



OPEECULAE,. Of, or belonging to, the operculum. A term 

 applied to the valves which compose the operculum of multivalve 



