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Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 289 RISSOA ERITIMA. (Plate XXIII. fig. 40.) Testa ovata, umbilicata, albo-pellucida, nitida; anfractus 4, sutura profunda discreti, convexi, duo supremi Icevis, c&teri striis spiralibus tenuissimis sculpti, ultimus magnus, sub-globosus; umbilicus falciformis, in medio lira tenuissima instructus; apertura rotunde ovata, superne acuminata, longit. totius \ cequans; peristoma continuum, vix incrassatum, ad basim columellas subeffusum vel indistincte stib-canaliculatum. Longit. 1§ millim., diam. 1. This is more widely umbilicated than R. soluta, Philippi, is more regularly spirally striated, has a slight indication of a sinus at the base of the columella, and also differs in other particulars. RISSOA AGAPETA. (Plate XXI. fig. 23.) Testa ovata, imperforata, nitida, subpellucida, lineis spiralibus fuscis interruptis ornata ; anfractus 5, convexi, duo supremi minuiissime subpunctati, ca?teri spiraliter sulcati, sutura profunda sejuncti; apertura ovata, superne leviter acuminata, longit. totius k haud cequans; peristoma tenue, margine columellari anguste reflexo, superne labro callo tenui juncto. Longit. 1 | millim., diam. fere 1. The microscopic sculpture of the apical whorls has a very pretty shagreened appearance. The spiral sulci are about five in number on the penultimate volution, and twelve on the last. The uninterrupted brown lines fall on the ridges between the grooves. R. de-picta, Manzoni, from Madeira, is an allied but larger form. RISSOA COMPSA. (Plate XXIII. fig. 41.) Testa ovata, inperforata, parum nitida, albida vel dilute fuscescens; anfractus 5, convexi, sutura profunda discreti, sulcis spiralibus fortibus (in anfr. penult, circiter 5, in ultimo ad 12) sculpti; apertura rotunde ovata, superne leviter acuminata, loncjit. totius \ haud a^quans; peristoma continuum, vix incrassatum, ad basim obsolete expansum. Longit. 2 millim., diam. 1. W h e n placed side by side, this species is seen to be a trifle larger than R. agapeta, and a little smaller than R. depicta. It also differs from both in colour, and is more strongly grooved than either. RISSOA WALLICHI. (Plate XXI. fig. 24.) Testa ovata, solida, alba, interdum zona rufa cincta, imperforata ; anfractus 5-6, primi duo spiraliter tenuiter striati, cceteri plani-usculi, carinis volventibus prominentibus (in anfr. superioribus tribus, in ultimo 7-8) instructi, sutura profunda sejuncti; apertura ovata, longit. totius ^ pernio superans; peristoma continuum, margine externo leviter incrassato, columellari antice subdilatato. Longit. 3 millim., diam. 1|. The red zone, when present, occupies the central part of the last |