OCR Text |
Show 310 MR. E. A. SMITH ON THE [Apr. 1, 5 subaquans; peristoma tenue, margine columellari leviter reflexo, superne labro callo tenui juncto. Longit. 2 millim., diam. 1. This species has more convex whorls than P. varicifera, to which it bears a general resemblance. Its spiral ridges also are finer, the aperture different, and the labrum has no external varix. RISSOA SIMULANS. (Plate XXIV. fig. 16.) Testa ovata, imperforata, alba vel pallide fuscescens; anfractus 4, convexi, primus et secundus spiraliter striati, sequentes transversis (in anfr. penultimo circiter 3, in ultimo 8-9) instructi ; apertura rotunde ovata, longit. totius ^ paulo minor peristoma continuum, vix incrassatum, margine columellari anguste reflexo. Longit. 1| millim., diam. 1. This is a shorter stumpier species than R. varicifera and has no postlabral thickening. RISSOA ORDINARIA. (Plate XXIV. fig. 17.) Testa ovata, solidiuscula, alba, imperforata, nitida; anfractus 4, convexiusculi, sutura mediocriter profunda, paulo obliqua sejuncti, spiraliter substriati ; apertura rotunde ovata, superne acuminata, longit. totius 5paulo superans ; peristoma continuum, leviter incrassatum, margine columellari dilatato. Longit. 1^ millim., diam. j|. This species, although so small, is certainly adult. The spiral striae are not numerous, and only visible on well-preserved specimens by the aid of a microscope. RISSOA .EQ.UA. (Plate XXIV. fig. 18.) Testa brevis, turrita, alba, vix rimata ; anfractus 5, primi duo convexi, Iceves vel spiraliter tenuiter striati, cceteri superne tabulati, angulati, carinis fortibus (in anfr. superioribus duabus, in ultimo senis) instructi, lineis incrementi tenuissimis sculpti; apertura ovata, longit. totius ^ haud cequans; peristoma continuum, margine extemo vix incrassato, columellari dilatato, reflexo, rimum umbilicalem formante. Longit. 2\ millim., diam. L|. This species closely resembles R. perfect a in form. It is, however, a little larger, is not spotted, and has seven keels on the body-whorl instead of five ; of these, the one nearest the suture is very fine and thread-like, the next two, which also pass up the spire, are strong and prominent, and the remaining four gradually lessen in thickness, the lowermost being very inconspicuous. The nucleus of this species is also different from that of R.perfecta, and the outer lip is not thickened in the same manner. RISSOA FENESTRATA, Krauss. Hab. Cape of Good Hope. |