On the Filamentous, Long-Horned Diatomaceæ, with a description of two new species

An examination of this singular organism, (the first of the family which has occurred in this country), and a comparison of it with the allied forms described by Ehrenberg and Dr. Bailey, afford materials calculated to extend and correct our knowledge of this rather doubtful group of Diatomaceæ. Mr. Wigham’s discovery will also, we trust, induce surviving labourers in the same field, to endeavour to add to our knowledge of existing species, as much must yet be brought to light before a satisfactory classification of this group can be effected.

Most of the described species have been found only in a fossil, or rather, if we may so term it, a deposit state ; and in this state it is clearly difficult to form a correct idea of either species or genera, since deposits give no information as to the Diatoms being in threads or solitary frustules.

From this circumstance, and a disposition to describe every variety of form, and even many fragments of Diatoms, as species, both species and genera have been multiplied to a perplexing extent. It appears probable that there are few, if any, instances of truly fossil Diatoms, but that all the so-called fossil species are only deposits from still-existing and living species ; and it is only when we have the living Diatom before us, that we can give any specific or generic characters that can be at all relied upon.^*

The discovery of a new and living species of Chœtoceros, and a careful examination of most of the species of this and several other allied genera, described by Ehrenberg as found in a fossil state, have satisfied us that most, if not all these, will, when found in a living state, turn out to belong to the singular filamentous and horned group, which may for the present, with some extension of its character (such as is hereafter attempted in this paper), be comprehended in the genus Chœtoceros.

The typical species of Ehrenberg’s genus appears to be C. didymus. This occurs not unfrequently in guano. The horns proceed immediately from apertures on each side of the frustules (an essential character of Ehrenberg’s genus), and differ in this respect from our newly-discovered species, in which the horns proceed from, or rather are an elongation of the intermediate rings.

Two species from the Antarctic Sea are briefly described by Ehrenberg (C. dichœta and C. tetrachœtd) ; each frustule is smooth, and the horns (of which the former species has two on each side, and the latter four) are very long and filiform. These species were, we believe, found in pancake-ice, and were brought home by Dr. J. D. Hooker.

Two species from Bermuda earth, marked as doubtful, are described by Dr. Bailey (C. bacillaria and C. diploneiis), and he has also recently described and figured a remarkable species, named by him C. boreale, found in the stomach of Botriodactyla grandis.^* The horns of this species are very long, and armed with numerous minute spines. Dr. Bailey describes and figures a small species also found in guano, named by him C. incurvum, which we have found plentiful in South American guano.

Of the allied genus Goniothecium, eight species are described by Ehrenberg, all found in the Richmond earth, North America. The two largest and most common are G. Rogersii and G. odontella, and we think it probable these will turn out, if discovered in a recent or living state, to be Chœtoceri. Of the remaining six species, we are led to conclude, from the discovery of the Breydon species, that two of them belong to the genus Chætoceros, and are, when living, filamentous. T hey are Goniotliecium gastridium, of which we have found many specimens with the horns perfect, and G. crenatum. A figure of a frustule of this species is given in the Microgeologie of Ehrenberg ; and it can scarcely be distinguished from the frustules of the Breydon species. Similar frustules are of frequent occurrence in African and other guano, and in several fossil earths of marine formation, and we have detected recent specimens in a gathering lately sent us from Monterey Bay, North America. Goniothecium hispidum and G. didymum of Ehrenberg, scarcely appear to differ from some of the smaller frustules of the Breydon species. G. navícula and G. barbatum are marked by Ehrenberg as doubtful species of Goniothecium ; but are clearly allied to G. crenatum, or our Breydon species.

Several other fossil genera of Ehrenberg contain species which will probably be found to belong to the long-horned filamentous Diatoms. Xanthiopyxis cingulata has precisely the cup-shaped and hispid character of our Breydon species, but is destitute of the neck. Syndendrium diadema and Dicladia capreolus are common species ; they are found with the other Chœtoceri, in various earths, and guano, and appear to be of the same family. They are chiefly distinguished by long styles, proceeding from the rounded end of the frustule, which styles are branched at the end, and are not unfrequently found with a portion of the membrane adhering to them, in which they seem to have been imbedded. Omphalotheca hispida has the appearance of an imperfect frustule, and Mastogonia prœtexta, of a semi-frustule of Goniothecium Rogersii.

We venture to give a synopsis of the Chcetoceri, adapted to our present imperfect state of knowledge of these singular organisms.

Filamentous ; filaments elliptical, fragile, imperfectly siliceous. Frustules without striæ, united in pairs by the interlacing on each side, of horns proceeding from the frustules, or from a cingulum between the frustules. Horns often of great length, and sometimes spinous, or serrated.

N. B.—To Ehrenberg’s description should be added, “Cornubus utrinque duobus.” This species clearly belongs to the genus Ghœtoceros. Many examples have occurred with the horns perfect. See Plate vii., fig.

Smithsonian Contributions, Feb. 1854, p. 9. Plate VII., figs. 9—11.

We have found this species abundant in guano.

Mr. Tufifen West has detected in guano frustules of a species, belonging to this section, which is new to me, and may perhaps be C. Bacillaria, Bailey. For figures of these frustules see Plate VII., figs. 1, 2.

1854, p. 8. Plate VII., figs. 12—15.

Horns proceeding from the centre of the circular end ; very stout and long, and beset with short spines, recurved.

In guano from Callao, occurring in small flakes or patches full of pieces of the horns, and a few detached frustules. Plate VIL, figs. 16—18.

§§§ Horns proceeding from, a cingulum or ring, dividing the frustules.

Frustules cup-shaped, with a band round the mouth of the cup, and a neck or bulb, proceeding from the centre Frustules beset with minute short spines, or papillae, in all parts, except the band. Oval, on a front, or end view, the spines appearing as minute specks. Boiled in acid, the filaments break up, and the frustules, in an isolated state, and detached rings, with the horns proceeding from them, are all that can be detected. The rings may readily be distinguished from the frustules seen endwise, as they are open, and without dots ; while the frustules, seen endwise, are dotted.

In brackish water, near Breydon, Great Yarmouth. Plate VII., figs. 19—36.

We have named this species after the discoverer, Mr. Wigham, an excellent practical botanist, indefatigable in the pursuit of his favourite study, and most liberal in his communications to his friends.

The C. Wighamii was, as before stated, found near the salt-water estuary, called Breydon, at the point where the rivers Yare and Waveney meet. It occurred in a gathering made from a dirty ditch of brackish water, at the back of a small public-house, called “The Burney Arms,” which is marked on the Ordnance maps. The gathering abounded in Campylodiscus dypeus (a species chiefly known before as occurring in fossil earth from Bohemia), and in one or more species of Mastogloia ; it also contained Bacillaria paradoxa, Amphora salina, Navícula palpebralis and tumens, Mdosira variares and stibflexilis, and the Viva bullosa (*); and Brotococcus hœmatodes (?) abounded also in it, with which last the Chœtoceros seemed most associated. It was perhaps parasitical on some Algæ, and, after being detached, had floated to where it was discovered. This place has been frequently visited since Mr. Wigham’s decease, and searched in vain, for the Chœtoceros ; although most of the above species

We have detected most of the species above described in guano (chiefly from Callao), and especially in little transparent flakes or patches containing a mass of frustules. C. gaxtridium, incurvum, JVighamii, and Peruvianum are of most frequent occurrence.

There can be little doubt that all the guano of the coast of Peru is in like manner pervaded with these organisms, and if so, we ought to look to this locality for living species. C. Wiqhamii has, as we have already stated, been lately gathered in Monterey Bay, and a careful search would probably bring other species to light.

The discovery of a number of specimens of C. boreale in the stomach of a large species of Holothuria, or Sea-Cucumber, should lead to the examination of the stomachs of Sea-Slugs, especially of such as are known to feed on marine Algæ, for specimens of this singular and interesting group of Diatomaceæ. were met with. In the living species of C. Wighamii, the endochromc was seen of a green colour, and aggregated in the centre of each frustule, in the manner represented in the figures of Encamjria zodaicus, in Kutz. Bac., Pl. XXL, fig. 21, and Pritchard’s Infusoria, Pl. XIII., fig. 43. No appearance of conjugation has been observed, nor have we been able to detect in this, or any other of the species, mentioned in this paper, which have come under our observation, any striæ, or markings of that kind.