220 OLIVELLA. 



OCTOMEEIS. Sow. (okt-w, octo, eight ; jxtpog, meros, part.) 

 Fam. Balanidea, Bl. — Order, Sessile Cirripedes^ Lam. — Bescr. 

 Eight principal valves circularly arranged, forming a compressed 

 cone, attached by a jagged base ; aperture enclosed by an oper- 

 culum, consisting of four valves in pairs. — Obs. The only genus 

 of Sessile Cirripedes agreeing with this in the number of prin- 

 cipal valves is Catophragmus, Sow. which is, however, sufficiently 

 distinguished by the several rows of smaller valves by which the 

 principals are surrounded at the base. O. angulosus. PI. i. 

 fig. 24. 



ODONTIS. Sow. MoNODONTA, Lam. 



ODOSTOMIA. Fleming, 1842. Bescr. " SheU conical ; aperture 

 ovate ; peristome incomplete, retrally, and furnished with a 

 tooth on the pillar." A genus originally composed of several 

 small species of land shells. Turbo plicatus, Spiralis, Uniden- 

 tatus, &c. Mont. Since applied to some minute marine shells, 

 nearly resembling Chemnitzia. Ex. O. plicata. PI. xxviii. fig. 

 587. 



OLIYA, Auct. {An olive.) Fam. Convoluta, Lam. Angyos- 

 tomata. Bl. — Bescr. Oblong, cylindrical, thick, smooth, shining ; 

 spire very short, with sutures distinct, aperture elongated, 

 notched at both extremities ; outer lip generally thick ; columella 

 thick, obliquely striated, terminated by a tumid, oblique, striated 

 varix ; a raised band passing round the lower part of the body 

 whorl. — Obs. The shells composing this well known genus 

 present a great variety of rich markings and brilliant colours. 

 They are marine and tropical. Possil species are fomid sparingly 

 in the London Clay and Calcaire-grossier. The AnciUarise are 

 distinguished from this genus by the sutures of the whorls being 

 covered by enamel. Mr. Eeeve's Monograph contains 99 species. 

 The genus is thus divided in the British Museum arrangement, 

 Stbephoka and Olivella, the O. porphyria and the common 

 form; Scaphtjla, the wide-mouthed cymbiform species, O. auri- 

 ciilaria ; Agaeonia, G-ray, the thin subulate species, with the 

 mouth widening at the bottom. PI. xxi. fig. 457. 



OLIVELLA. Sw. A genus of " Olivinse," Sw. thus described : 



