OF THE 34808- MICROSCOPICAL SOCIETY OF LONDON. NEW SERIES. VOLUME XIII. LONDON: JOHN CHURCHILL AND SONS, NEW BURLINGTON STREET. TRANSACTIONS. DESCRIPTIONS of NEw and RARE DIATOMS. SERIES XIV. By R. K. GREVILLE, LL.D., F.R.S.E., &c. (Read Nov. 9th, 1864.) (Plates I & II.) PLAGIOGRAMMA. Plagiogramma Wallichianum, n. sp., Grev.-Valve linear, rounded at the ends; costæ two in the middle, and one each end, with a few intermediate pervious striæ. (Figs. 7, 8.) Hab. St. Helena; rare; Dr. Wallich. A minute, but well-marked species, of which I find a characteristic sketch of the valve in Dr. Wallich's note-book. I have also obtained views of the frustule in both aspects, in the portion of the dredging he was kind enough to place in my hands. It is not very closely allied to any described species, differing materially from P. pygmæum, to which it approaches in size, in the pervious striæ, and strictly linear form. Length C017". PYXILLA, n. gen., Grev. Frustules free, oblong, transversely bivalved, box-like, minutely cellulate; each valve terminating in a short, thick apiculus. This genus must obviously be associated with the Pyxidicula; indeed, the two species of which it is composed, might almost have been placed in Pyxidicula itself, so loosely VOL. XIII. a is that genus at present defined. In both sections, as it stands (including both Pyxidicula and Dictyopyxis of Ehrenberg), there are, according to my view, species bearing little, if any, generic affinity; and, as the minute fossil diatoms I am about to describe, possess a striking character of their own, I prefer to keep them apart, rather than add to the existing uncertainty and confusion, which, after all, is mainly owing, as my friend Mr. Ralfs has remarked, to various so-called species being still little known. Pyxilla Johnsoniana, n. sp., Grev.-Frustule cylindricaloval, simple (no contraction at the suture). (Fig. 6.) Hab. Barbadoes deposit, Cambridge estate; in slides communicated by C. Johnson, Esq.; very rare. This rare species has only occurred to me twice, but it is highly probable that in some other samples of the deposit, both it and the following may be more frequent. The cellulation is so minute as to be correctly defined as punctate; but the cellules, when sufficiently magnified, appear to be regularly hexagonal. The suture is situated at somewhat more than one third of the total length from one extremity. Length of frustule '0025". Pyxilla Barbadensis, n. sp., Grev.-Frustule contracted at the suture, one valve cylindrical, the other globose. (Fig. 5.) Hab. Barbadoes deposit, Cambridge estate; in slides communicated by C. Johnson, Esq. A most beautiful diatom. The globose valve with its contracted base and terminal apiculus, resembles the bulbous dome which crowns the minaret of an eastern mosque. Although there is a great contraction between the valves, the suture itself is acute and somewhat prominent, as in some of the Creswelliæ. The punctation is as minute as in the preceding species, and, under a high power, comes out equally beautiful as hexagonal reticulation. Length 0030". CRESSWELLIA. Cresswellia Palmeriana, n. sp., Grev.-Very large; frustules in front view short, cylindrical, with truncate ends; connecting processes numerous, truncate; cellules puncti. form at the suture, becoming larger and hexagonal towards the ends. (Fig. 9.) Hab. Hong Kong harbour, John Linton Palmer, Esq.; Shark's Bay, Australia, in stomachs of Ascidians; Dr. Macdonald. The largest and finest of all the known Cresswelliæ, discovered by my acute and very obliging correspondent, Mr. J. Linton Palmer, Surgeon, R.N., who has kindly transmitted many new things, accompanied with notes and sketches. One large diatom of singular interest I hope shortly to publish as a new genus, under the well-merited name of Palmeria. The subject at present under consideration is a giant in Cresswellia, the frustules being no less than 0030" to 0035" long, and 0040′′ broad, somewhat contracted towards the suture. The connecting processes are twenty and upwards, and truncate, as in C. Turris and turgida, and situated just within the margin of the truncate end of the valve. A very remarkable character is conspicuous in the structure, which, near the suture, is punctate, but, by degrees, becomes more and more distinctly cellulate, the cellules towards the ends being hexagonal, and about ten in '001". I have as yet seen only two frustules in connection. While engaged in preparing this paper, I was agreeably surprised to discover in some Shark's Bay slides, in the cabinet of my friend, Mr. George Norman, both front and side views of this species. For the finest example in my own cabinet, I am indebted to the generosity of Lawrence Hardman, Esq., the well-known diatomist and admirable microscopical manipulator, whose friendly assistance in some very critical investigation, I shall hereafter have a more favorable opportunity of acknowledging. Cresswellia cylindracea, n. sp., Grev.- Frustules cylindrical (not contracted at the suture), truncated, unequal in length; connecting processes numerous, fine, truncated; structure obscure. (Fig. 10.) Hab. Hong Kong harbour; May and June; John Linton Palmer, Esq. Another very notable species, which we owe to the exertions of Mr. Palmer. It exhibits a larger number of frustules in connection than any other hitherto observed, and, at first sight, bears no inconsiderable resemblance to a Melosira. The connecting processes, and even the suture, are inconspicuous in specimens preserved in balsam, but come out more distinctly when burnt on the cover and mounted dry. The structure is dense and obscure, the colour pale, with a tinge of yellow. It is by no means rare in one of the gatherings kindly sent me by its discoverer. Length of frustules 0015" to 0025", or more; breadth about 0018". Cresswellia Barbadensis, n. sp., Grev.-Small; frustules elliptic, conspicuously cellulate; suture sharply prominent; |