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Show 714 MR. E. A. SMITH ON SHELLS FROM LAKE NYASSA. [Nov. 6, ber about sixteen in the last whorl; the granules are produced by transverse sulci, which cut the ribs at right angles ; they are squarish and four or five in number on the ribs of the upper whorls, and the same on the body-whorl, where they terminate about its middle, beneath which the spiral ridges between the sulci are simple, and rather finer than those at the upper part of the volution; aperture acuminately ovate, occupying rather more than one third of the entire length of the shell. Length 18 millims., diam. 6-J. This species must not be confounded with M. nodicincta, Dohrn, also found at Lake Nyassa. Although in sculpture there is certainly much resemblance, the very different form and proportion of the whorls indicate the specific distinctness of this pretty shell. The spire is produced to quite an acute apex ; and its outlines are rectilinear. The nodules on the ribs are large for the size of the species, squarish, and in oblique curves. The red dots are for the most part situated in the interstices between the ribs, at the base of each nodule, thus forming both longitudinal and transverse series. 5. MELANIA POLYMORPHA. (Plate LXXV. figs. 4-10.) Shell elongate, pyramidal, thin, under a pale-olive epidermis, whitish, spotted with reddish brown ; whorls 8-9, almost flat, sometimes somewhat convex, margined above at the suture, which is deep and subcanaliculate, either with or without longitudinal plicae, nodulous through being intersected by a few transverse striae ; the plicae are usually only on the upper whorls, but in some specimens there are traces of them on the last, or they are well developed; the body-whorl is generally sculptured with 3-4 spiral sulci at the periphery, and by other less distinct striae above and below it; aperture ovate-acuminate above, varying in length, occupying either a little more or less than half the entire shell, pale horn-colour, spotted with reddish brown. Length 16 millims., diam. 5\. Another specimen 14 millims. long, and 4\ wide. The form of this species is subject to great variation ; and the extremes, taken apart from intermediate varieties, have decidedly the aspect of distinct species. The sculpture is also very different in certain specimens, some being almost smooth, with the exception of the spiral sulci on the body-whorl, and a few less distinct striae on this and the upper volutions. Others are distinctly ribbed, the ribs being cut across by two spiral striae in the upper whorls, thus producing three granules on each rib, the uppermost situated at the suture on the thickened margin. This incrassation is constant in all specimens ; and so is the deep suture, which gives the spire a turreted aspect. Six small examples have the thickened margin very strongly developed, the longitudinal ribs particularly granulous, and present on the body-whorl, terminating at the periphery, where they are limited by a few distinct spiral sulci. The disposition of the reddish-brown spotting and markings is not constantly the same. Generally a series of dots, short, rounded, |