OCR Text |
Show Ib71.] MR. HARPER PEASE ON POLYNESIAN LAND-SHELLS. 469 As the two species have been confounded by many collectors, furnish a detailed description of each, drawn up from mature specimens, of which I have had an opportunity of examining a large number. PLECOTREMA STRIATA, Phil. Auricula striata, Phil. Zeit. f. Mai. 1846, p. 98. Plecotrema striata, Pfr. Mon. Auric. 1856, p. 104. T. crassa, imperforata, globoso-conica, subovata, nigra, spiraliter impresse striata, striis rare ineequaliter distantibus, interstitiis planis, striis remote hispidulis; spira conica, mucronata, con-vexiuscula; sutura linearis; anfr. 7, ultimus tumidiusculus, \ longitudinis testce fere eequans, basi vix attenuatus; apertura fere verticalis, oblonga, postice acuta, vix contracta, basi rotundata, nigricans vel cinereo-nigrescens ; plicee parietales 2, lamelli-formes, superior per obliqua, altera extus bifida, valde compressa, elevata, profunde intrans ; plica columellaris valida, transversa; peristoma rectum, acutum, marginibus plerumque callo lato tenuis-simo junctis, dextro intus, dimidio anteriore et circa basin prope marginem calloso, bidentato; columella extus ad marginem vix elevuto-laminata, infra juxta regionem umbilicalem vix crispata. Dimens. 8 X 5, vel 5 X 3 mill. Hab. Insula Oahu. This species is constant in its characters, and distinct from all varieties of P. clausa, H. & A. Ad.; the shell is black, solid, engraved concentrically with impressed strise, which are generally regular; but occasionally one is omitted, leaving the interspaces wider ; the interstices are flat; the last whorl is swollen, about one half the length of the shell; the aperture is very slightly oblique, acute posteriorly, more so than in P. clausa, and in some specimens constricted, caused by a depression around the upper part of the last whorl near the suture ; the lamellae on the inner lip are oblique, more compressed and prominent than in P. clausa, the lower one especially, which passes round far within the aperture; the outer lip on its edge is acute, on its anterior half and around the base, just within the margin, it is slightly callous, on which part the teeth are placed, which are smaller than those in P. clausa. The columella is bordered by an elevated lamina; the aperture is blackish or dark cinereous; the teeth and lamellae white; the stria? are furnished with remote bristly hairs. The characters by which the above may be readily distinguished from P. clausa are its black colour, larger size, dark aperture, not being ribbed or lirate but striate, the aperture being more open, the lamellae on the wall of the aperture compressed and prominent, the teeth on outer lip smaller and the callosity not so thick. These characters are constant, even in specimens of the smallest size. PLECOTREMA CLAUSA, A. Ad. T. imperforata, ovato-conoidea, crassa, vix nitidula, spiraliter costulata aut lirata, costis rotundatis, interstitiis setulis munitis |