II.-On some New Genera and Species of Diatomaceæ.

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.

2.

australis (P. Petit), n. sp.; a, frustule; b, inferior valve; c, superior do.

3.--Cocconeis Wrightii (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. x 200 diameters; a, valve; b, f. v. of do.

16.-Stauroneis robusta (P. Petit), n. sp.; a, valve; b, frustule.
17.-Amphiprora rugosa (P. Petit), n. sp.
18.-Surirella Filholii (P. Petit), n. sp.

19. Trachysphenia australis (P. Petit), n. gen. and sp.

20.-Grammatophora marina (Kg.), n. var.

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,† 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 = 25 μ 339.

† 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 Diatomacea.'

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 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.

H. lævis, Ehr., and H. patagonicus, Ehr., are only known to me through the very imperfect figures in the Mikrogeologie.'

Apparently allied to H. maximus and Pyxidicula radiata is Weise's Craspedodiscus radiatus.* His figure represents a disk with a large umbilicus on which a number of distinct granules are concentrically disposed; the remainder of the disk has very fine radiating striæ; the diameter of disk (× 300) according to his figure is exactly one inch, diameter of umbilicus. If these forms be distinct, their specific names must be changed, as they all undoubtedly belong to one genus.-F. K.]

AMPHORA, Ehr.

5. A. Schmidtii (P. Petit). 'A. S. Atlas,' pl. xxviii. fig. 51, without name or diagnosis. Valves cymbiform, slightly turgid at the centre of the ventral margin (du côté le moins courbe); extremities rounded; median line faintly curved. Striæ transverse, on the dorsal side (du côté le plus courbe) of the median line short, distinct, submarginal, slightly radiant, not reaching the median line by a length equal to the diameter of the valve; striæ on ventral side very short, close to but not touching the median line, interrupted opposite the centre by a blank space. Median line subcentral. Length 88 μ, breadth 15 μ 4.

Foveaux Strait.†

6. A. cristata (P. Petit). Valves cymbiform, with capitate extremities suddenly contracted below the apices; ventral margin abruptly inflated at the centre, median line very close to this margin. The dorsal margin has a large crenated ridge, the crenations of which gradually decrease in breadth as they approach the apices. Striæ distinct, parallel on the valve radiating on the ridge: about 25 in 25 μ. Average length 77 μ, greatest breadth with the ridge 19 μ.

Very abundant in Foveaux Strait. Pl. XIV., Fig. 8.

This beautiful species approaches very near to A. sinuata in outline, but differs in the valve being distinctly divided into two parts, the valve proper, and the so-called ridge; it is also larger.

7. A. aspera (P. Petit). Valves cymbiform, with extremities attenuated, sub-capitate, rounded, and slightly recurved; median line for the greater part of its length and the central nodule obscured by the ventral margin. Striæ punctate, radiant, resembling those of Stauroneis aspera, reaching the median line on the dorsal side. Length 57 μ 2, breadth 13 μ 2.

Foveaux Strait. Pl. XIV., Fig. 9.

This species resembles A. rhombica,‡ but differs in size, and the extremities are recurved.

*Bull. Imp. Acad. St. Petersburg,' vol. vi. p. 311, pl. ii. fig. x.

+ Foveaux Strait, New Zealand; lat. 46° 40' S., long. 168° 10' E.
Kitton, Schmidt's Atlas,' pl. 40, fig. 39.

EPITHEMIA, Bréb.

8. E.? monilifera (P. Petit). Valves arched, covered with large moniliform granules, 2 μ 2 in diameter, irregularly disposed, often with stout transverse radiant costa. [The few specimens I have seen never had more than three.-F. K.] Length 72 μ 6 to 188 μ 4, breadth 15 μ 4.

Foveaux Strait. Pl. XIV., Fig. 10.

This species very much resembles Schmidt's Amphora monilifera,* which he doubtfully refers to A. monilifera of Gregory;† but as neither median line nor central nodule is present, it must be placed among the Epithemias. The transverse costa present on some individuals confirm this view. On the other hand, the characters are not well marked, and the connecting zone is indistinct, making us doubt the bivalvular nature of the siliceous envelope. We ought, perhaps, to consider this organism as much a Polycystin as a diatom. [The resemblance to A. monilifera does not seem to me very apparent; it more nearly approaches Grunow's Euodia Frauenfeldii.—F. K.]

NAVICULA, Ehr.

This

9. N. quærnerensis (Grun.), var. dilatata, P. Petit. variety is distinguished from the type by its larger size and scarcely produced apices; the striæ are subradiant and very delicate; this character, together with the general aspect of the valve, will not permit us to consider this form as anything else than a variety of Grunow's species. Length 33 μ, breadth 37 μ 6. [Query, should not these figures be transposed ?-F. K.] Striæ, 40 in 25 μ.

Campbell Island. Pl. XV., Fig. 24.

10. N. Campbellii (P. Petit). Valves lanceolate, with concave margins; extremities cuneiform; apices rounded; median line straight; central nodule indistinct, surrounded by a circular blank space. Striæ distinct, slightly radiant at the centre, parallel towards the extremities, reaching median line, excepting at the centre; no longitudinal striæ. Length 84 μ 4, breadth 22 μ; 18 to 20 striæ in 25 μ.

Campbell Island. Pl. XV., Fig. 23.

This species is closely allied by its form to N. constricta, Grunow, but differs from that species in the striæ reaching the median line.

11. N. biseriata (P. Petit). Valves lanceolate, extremities attenuated, apices rounded, median line not reaching the ends of the valve, central and terminal nodules distinct. Striæ radiant interrupted, absent on one side of the central nodule resembling a

*Atlas,' pl. 26, fig. 32.

Diatoms of the Clyde.'

Verh.,' 1860, p. 355, fig. 18.