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Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 285 LACUNA PUMILIO. (Plate XXIII. fig. 31.) Testa minuta, albida, late umbilicata, subglobosa, incrementi lineis obliquis striata, aliis spiralibus obsoletis subcancellata; tres, convexi, ultimus supra tabulatus et subangulatus, inferne carinis duabus ductus; apertura irregulariter ovata, magna, longit. totius f adcequans ; columella fere rectilinearis, anguste reflexa, inferneproducta, carince umbilicum circumdanti juncta. Longit. 1| millim., diam. Ii. Although so small, this does not look like a young shell. Of the two keels on the base of the body-whorl, that bordering the umbilicus is the more conspicuous, and unites with the lower extremity of the columella; the other runs into the base of the aperture, a little farther off, and the space between is somewhat flat. FOSSARUS AMBIGUUS (Linne'). Hab. Many parts of the Mediterranean, the coast of Morocco, Cape Verde Islands and Senegal, Madeira and the Canary Islands. The specimens from St. Helena, which I believe belong to this species, present a very great variation in form. Some closely resemble Adanson's figure (Senegal, pi. 13. fig. 1), but are rather more widely umbilicated. The majority, however, have the spire scarcely elevated above the body-whorl, the mouth large, and the umbilicus very open, so that, in many cases, the body-whorl is detached from the preceding for a short distance. The spiral keels, also, are very variable in number and thickness, but all specimens exhibit very much the same kind of fine spiral striae upon and between the ridges. I see no reason for separating F. cumingii oi A. Adams from this species; and F. bicarinatus of the same author may also be an extreme form of it. FOSSARUS (COUTHOUYIA) DENTIFER. (Plate XXIII. fig. 32.) Testa parva, alba, minute rimata, solida, haud nitens; anfractus 5-6, apicalis globosus, involutus, cceteri convexi, superne obsolete angulati, lineis incrementi rugosis obliquis striati; anfr. ultimus magnus, globosus, liris spiralibus distantibus paucis (circiter sex) ductus ; apertura subcircular is, longit. totius i adcequans labrum tenue, superne haud sinuatum; columella arcuata, callosa, infra medium transverse plicata, infra plicam late excavata. Longit. 2 millim., diam. max. 1|. The general character of this shell seems to refer it to this genus, but it differs from other species iu having a columellar denticle. The genus Plicifer of H. Adams (Proc. Zool. Soc. 1868, p. 293) was founded for a small white shell with a somewhat similar tooth or fold on the pillar. P. nevilli, however, has a posterior sinus to the labrum, and differs in other respects from the present species. FOSSARUS (COUTHOUYIA) L-EVIUSCULUS. (Plate XXIII. fig. 33.) Testa parva, anguste umbilicata, ovata, superne acuminata, alba, PROC. ZOOL. SOC-1890, No. XX. 20 |
