OCR Text |
Show 1879.] CMC1UM OF T H E 'CHALLENGER' EXPEDITION. 807 tissime et irregulariter transversim striata; apicem versus paululo tumidula. Apertura obliqua, haud marginata. Length 2*3 m m . Breadth 0*2 m m. The apex of this specimen has been broken and restored; so that its original form is somewhat obliterated. The species presents the usual slight swelling at the beginning of the curve, a little way from the apex. It has three curvatures. The aperture is oblique. From P. asturiana (see 'Les Fonds dela Mer,' vol.i. pp. 174 and 218, pi. xxix. fig. 7) it differs in that the shell here is shorter, tbe curves stronger, while the annular striations are much finer and are differently arranged. Its form distinguishes it from P. cornucopiee ('Les Fonds,'&c. vol. i. pp. 122,174, 218. pi. xv. figs. 7-9). The absence of the characteristic apex is a feature noticeable here, as well as in some specimens of P. asturiana which yet present all the other characteristics of the genus. In a shell so sharp at the point a fractured apex is not wonderful; it doubtless occurs through accident; and the injury is repaired, and the ^traces of it concealed, by deposition of shelly matter. 2. STREBLOCERAS SUBANNULATUM, n. sp. July 1875. Reefs off Honolulu. 40 fms. Three specimens. Testa minuta, bicurvata, vitrea, diaphana, nitida ; nucleo spirali, obliquo ; anfractibus duobus ; postea testa tubularia, latitudine accrescens, curvam duplicem sequens, transversim subannulata, annulis latis, minutissime expressis, subacutis, late separatis. Apertura obliqua. Length 3 m m . Breadth 0*5 m m. These three specimens are the first living representatives of the genus; and that they really belong to it is obvious, since the nucleus exhibits two or two and a half whorls and is placed at the side, not in the central plane of the shell-the position occupied by the nucleus in Ceecum with as many whorls, and in Parastrophia with only half a whorl; and this is a distinction of great importance. Below the nucleus the shell increases steadily in breadth, and as it lengthens takes a curve in two planes. The shell is vitreous, translucent, glossy, and thin, ornamented by broad, remote, transverse slightly sharp undulations, which can hardly be reckoned rings, being so faint as only to be visible under the microscope. This ornamentation, slight as it is, is very characteristic. The mouth is oblique, with the obliquity turned towards the plane of tbe apex of the nucleus. This is a feature of some importance in the family of Csecidee, the direction of the oblique mouth being constant in the well-known genera Ceecum and Meioceras; and the same may be affirmed of Parastrophia. WATSONIA, nov. gen. Testa probabiliter primum nucleosa, postea tubularia, decollata, bicurvata conica; apertura orbicularis, valde obliqua, valide circumdata. The three specimens here under consideration have all tbe PROC. ZOOL. Soc-1879, No. LII. 52 |