II.—On some New Genera and Species of Diatomaceœ. By M. P. PETIT. Translated by F. Kitton, Hon. F.R.M.S., by the kind permission of the Author. (Taken as read before the ROYAL MICROSCOPICAL SOCIETY, June 5, 1878.) PLATES XIV. AND XV. IN the Fond de la Mer' M. P. Petit has given a list of Diatomaceæ collected by the expedition sent by the French Government to Campbell Island,* in the year 1874, for the purpose of observing the transit of Venus. Dr. Filhol, one of the gentlemen appointed by the Government, after leaving the expedition, travelled alone in New Zealand, and the forms obtained by him are also included in M. Petit's list. DESCRIPTION OF THE PLATES. PLATE XIV. FIG. 1.-Cocconeis notata (P. Petit), n. sp. 33 2. australis (P. Petit), n. sp.; a, frustule; b, inferior valve; c, superior do. 3.--Cocconeis Wright (O'M.), new form. 4. Crux (Ehr.). 5.-Campyloneis Grevillii (Grun.); a, frustule; b, one of the plates of the inferior valve; c, second plate of do.; d, superior valve. 6.-Rhaphoneis fasciolata (Greg.), n. var. 7.-Hyalodiscus maximus (P. Petit), n. sp. × 200 diameters; a, valve; b, f. v. of do. 16.-Stauroneis robusta (P. Petit), n. sp.; a, valve; b, frustule. 19. Trachysphenia australis (P. Petit), n. gen. and sp. 20.-Grammatophora marina (Kg.), n. var. 21. 24. longissima (P. Petit), n. sp. 22.-Rhabdonema hamuliferum (Kitton), n. sp. 23.-Navicula Campbellii (P. Petit), n. sp. quærnerensis (Grun.), var. dilatata (P. Petit). 25.-Auliscus stelliger (P. Petit), n. sp. All the figures, excepting Fig. 7, are × 600 diameters. *Campbell Island is in the South Pacific; lat. 52° 33' S., long. 169° 8' E. (London). It is of volcanic origin, 36 miles in circumference, and 1500 feet above the sea-level. COCCONEIS. 1. C. notata (P. Petit). Valves ovate, median line sigmoid, central nodule dilated into a smooth band (pseudo-stauros) reaching the margin and terminated at one margin by a circular hyaline enlargement. Striæ transverse, very close, subradiant, and finely punctate, reaching median line. Length 26 μ 4, breadth 13 μ 6. Lyell's Bay. Pl. XIV., Fig. 1. 2. C. australis (P. Petit). Valves dissimilar, small suborbicular, the inferior (Fig. 2b) having a sigmoid line. Striæ longitudinal, close. The superior valve (Fig. 2c) smooth, but furnished with short distant marginal coste (closely resembling the canaliculi of the Surirella). Length 26 μ 4, breadth 24 μ 2. Lyell's Bay. Pl. XIV., Fig. 2. μ 3. Raphoneis fasciolata, var. australis (P. Petit). This form shows characters differing from the type. The rows of granules increase in length as they approach the centre, producing a very marked contraction in the smooth space occupying the centre of the valve. This variety is very variable in shape and size, its length varying between 28 μ 6 and 55 μ. Lyell's Bay, where it is very abundant, but it does not occur in other localities. Pl. XIV., Fig. 6. HYALODISCUS, Ehr. (Cleve emend.: Diatoms from the Arctic Sea, p. 4.) Note on the Genus.-M. Cleve has already verified the affinities of all the discoid species with a central fracture or umbilicus. These he has correctly united in a single genus Hyalodiscus of Ehrenberg. We have moreover remarked, that in all the species placed in Podosira the zone is curved in an opposite direction to that which exists in P. Montagnei. In examining H. hormoides (P. hormoides, Ktz.) living, we have seen that the endochrome has nothing in common with that of the true Podosiræ; it is granular, as it is in the Melosire to which it belongs. The endochrome in H. hormoides forms a single plasmatic layer with four lobes, and always resembling in disposition the endochrome of Achnanthidium; it is only in contact with one side. These characters clearly indicate that H. hormoides ought to be classed with the Achnanthem if we follow the system of classification proposed in our list of diatoms,f and it is probable other species of the genus exhibit the same peculiarities if we had the opportunity of studying them. 4. H. maximus (P. Petit). Valves discoid, very large, central * 1 μ = 0001 of a metre, 001 of an English inch † See 'M. M. J.,' vol. xviii. p. 10. Eulenstein has previously published a species which he has named maximus. See Habirshaw's Catalogue of the Diatomaceæ.' umbilicus occupying one-third of the entire diameter; the valves appear striated under a low power, but when more highly magnified the puncta are seen to have a quincuncial arrangement; a ring of crossed striæ surrounds the margin; zone narrow and curved. Diameter 70 μ 4 to 130 μ, umbilicus about 25 μ to 50 Ο μ. Campbell Island. Pl. XIV., Fig. 7. This species is very variable in size; the umbilicus is dark in colour; with a low magnification the striæ appear radiant, but under high-power objectives the puncta are found to be arranged in quincunxes. This arrangement, and the absence of dark robust striæ starting from the umbilicus, distinguish this species from H. radiatus (Pyxidicula radiata, O'Meara*). [M. Petit is correct in placing Podosira hormoides and P. maculata in the genus Hyalodiscus. Herr Cleve and M. Petit are, however, incorrect in making a distinct species of H. maculatus (P. maculata, Wm. Smith); it is identical with H. stelliger, Bailey, of which I have seen authentic examples (and perhaps with Craspedodiscus stella, Ehr.). Professor H. L. Smith also confirms this.t It appears very doubtful to me whether H. subtilis of Bailey is the same as H. Franklinii: his figure represents a form with a small umbilicus and two sets of curvilinear striæ intersecting each other like the engine-turning on the back of a watch. H. Franklinii (probably the same as H. californicus) has very fine radiating striæ, certainly invisible with the objectives used by Bailey twenty years ago. H. subtilis is a much smaller form than the preceding: my specimens (from the English Channel and the Sandwich Islands) do not exceed in size the smallest valves of H. Franklinii, and the diameter of the umbilicus is not more than one-half the diameter of that in H. Franklinii. Discoplea umbilicata, Ehr., is perhaps the same as H. hormoides. M. Petit refers Coscinodiscus punctulatus, Greg., to H. stelliger. With this I do not concur; Gregory would, I imagine, have been well acquainted with Podosira maculata of the 'Synopsis'; moreover, his figures and description § do not agree with H. stelliger. In one of the Tuscarora' soundings I have occasionally seen a disk only differing from Actinocyclus interpunctatus (Brightwell) in having a very small umbilicus. It also occurs in a gathering from the island of St. Paul, a slide of which was kindly sent me by M. Petit. *Jour. of Linn. Soc.,' vol. xv., "Diatom. Kerguel.," p. 56, pl. i. fig. 9. † American Journal of Microscopy,' vol. ii. p. 149. Smithsonian Contributions,' vii. p. 10, f. 12, 1853. 'T. M. S.,' vol. v. pl. i. fig. 48; Clyde Diatoms,' p. 28, pl. ii. fig. 46. |