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Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 309 MARGINELLA (VOLVARIA) ZONATA, Kiener. The single specimen from St. Helena is small, about the same size as the form described by Krauss (Sudafr. Moll. p. 126) under the name M. dunkeri, but the labrum at the upper extremity is united with the shell at the suture and not below it. The position of this point of juncture, judging from the series of specimens in the Museum, is variable, and consequently when it is high up at the suture the upper margin of the brownish-yellow band will fall further below than when the end of the labrum is attached further down or below the suture. I am therefore of opinion that M. dunkeri should be regarded as a variety of M. zonata and not as a distinct species, as the distinctive features referred to by Krauss are not constant. Weinkauff (Monograph of Marginella, Conch.-Cab. ed. 2, p. 28) quotes this species as M. dunkeri from Ascension Island, his specimens being almost as large as typical examples of M. zonata, which appear to be common at the Cape of Good Hope. MITRA SIMPLEX, Dunker. Hab. Cape of Good Hope. RISSOA PLATIA. (Plate XXIV. fig. 13.) Testa minuta, ovato-turrita, imperforata, albida; anfractus 4\, superne concave excavati, in medio subacute angulati, infra angulum contracti, spiraliter lirati; apex obtusus, involutus; apertura rotunde ovata, superne acuminata, longit. totius j subaquans; peristoma continuum, incrassatum., subeffusum, margine columellari inferne subproducta. Longit. 1| millim., diam. 5. The spiral sculpture is continued upon the apical whorl, which is involuted, thus producing a very blunt top to the shell. The lirae are four to six in number on the lower half of the penultimate whorl, and rather coarser than those above the angle. RISSOA ATOMUS. (Plate XXIV. fig. 14.) Testa minuta, alba, pellucida, nitida, ovata, imperforata; anfractus 4, convexiusculi, laves, ultimus magnus ; apertura sub-pyriformis, longit. totius § adaquans; peristoma continuum, margine externo leviter patulo et incrassatq, columellari obliquo, superne valde calloso. Longit. 1 millim., diam. |. This minute species, of which there are three specimens, is certainly full-grown, and has no other sculpture except microscopic lines of growth. RISSOA VAGA. (Plate XXIV. fig. 15.) Testa minuta, tenuis, subrimata, dilute fuscescens, spiraliter lirata anfractus 5, convexi, liris filiformibus sp>iralibus (in anfr. penult. 3, ultimo 10) instructi; apertura ovato-rotumlata, longit. totius |