the evidence now before us, in removing the Monticuliporida from the Actinozoa, and that we may provisionally regard them as a special group of Alcyonaria. It should also be borne in mind in this connection that we are at present quite unacquainted with the animal of Heteropora, and that it is just possible that an examination of the soft parts of this type -admittedly a very aberrant form of the Polyzoa-might show it to be a Cœlenterate. At the same time, I do not at all mean to deny but that some of the fossils which have been described by various palæontologists under the names of Monticulipora, Fistulipora, or Callopora, are probably really Polyzoa. Erroneous determinations of this kind, especially where microscopic examination has not been resorted to, are almost inevitable; but they do not affect the systematic position of the forms which are recognised as the types of Monticulipora and of the genera related to this.

260

CHAPTER XIII.

GENERA OF CHÆTETIDE AND MONTICULIPORIDE.

CHÆTETIDÆ,

Genus CHATETES, Fischer, 1837.

(Oryct. de Gouv. de Moscou, p. 159.)

Gen. Char.-Corallum massive, composed of long irregularly prismatic erect corallites, which are closely contiguous, and are completely amalgamated by means of their walls. Corallites of one kind only, opening upon the surface by means of irregularly polygonal, non-oblique calices, and destitute of true septa. Walls imperforate. Tabulæ complete, comparatively remote, often placed at corresponding levels in contiguous tubes. Visceral chamber often partially divided by an imperfect longitudinal septum (or by two such septa) resulting from the uncompleted fission of the tube into two young corallites.

Obs. It is not necessary to enter here into a detailed account of the genus Chatetes, except in so far as concerns its relations with the genera Stenopora, Lonsd., and Monticulipora, D'Orb., and even on this point little need be said. The type of the genus Chatetes is unquestionably the great C. radians, Fischer, of the Carboniferous Limestone of Russia, and the characters of the genus must, therefore, necessarily be based upon this species. This form was for the first time adequately

described by Mr Lonsdale (Geol. of Russ., vol. i. p. 595, 1845), who drew special attention to the fact that the walls of the corallites are inseparably united, so that fractures expose the interior of the tubes, this structure depending upon the fissiparous mode of increase of the coral. M'Coy (Brit. Pal. Foss., p. 82, 1851) may be considered as entirely accepting Mr Lonsdale's views as to the characters of the genus Chatetes. MilneEdwards and Haime (Brit. Foss. Cor. Intr., p. 61, 1850), while accepting the genus, ignore the feature just alluded to as so strongly emphasised by Mr Lonsdale, and add no character which could be accepted as in any way of generic value. In the "Polypiers Fossiles" (p. 261, 1851) the same authors give a fuller account of Chatetes, and they now unite with it the genus Stenopora, Lonsd., and also the ill-characterised type which D'Orbigny had named Monticulipora (Prodr. de Paléont., t. i. p. 25, 1850). At a still later period (Brit. Foss. Cor., p. 264, 1854), the two distinguished French observers so far altered their views that they accepted Monticulipora, D'Orb., as distinct from Chatetes, Fischer, the ground of distinction being that in the former the corallum increases by gemmation, whereas in the latter the mode of growth is by fission. Most subsequent writers have followed the course ultimately adopted by Milne-Edwards and Haime, so far as concerns the generic distinctness of Chatetes and Monticulipora, and the grounds of this distinction. In a paper, however, upon the species of Chatetes in the Lower Silurian rocks of North America (Quart. Journ. Geol. Soc., vol. xxx. p. 499, 1874), I formerly expressed the opinion that the genera Chatetes and Monticulipora were not sufficiently differentiated, and that the mere mode of growth, even if admitted to be of generic value, was a character so difficult, in many instances, of determination, that it should not be regarded as of itself sufficient to separate two types otherwise closely allied. At the same time I stated that I thought Stenopora, Lonsdale, to be insufficiently characterised, and pointed out that different observers had defined this genus by means of very different and in some cases compara

tively trivial features. To the opinions expressed in the paper just referred to I still adhere-in the sense, that is, that I still think the conclusion which I had then reached the only one justified by the information at that time published. Since that time, however, I have had the opportunity of making a careful microscopic examination of authentic Russian specimens of C. radians, Fischer, the type of its genus, and I am now quite satisfied as to its generic distinctness; while a similarly minute investigation of Monticulipora and its allies has convinced me that here also we have to deal with a distinct generic type. Lastly, as has been previously shown, I have had now the opportunity, in association with my friend Mr R. Etheridge, jun., of examining authentic Australian specimens of Stenopora, Lonsd., and have thus been able to show that this genus is one quite distinct from either Chatetes or Monticulipora, and, in reality, referable to the Perforate group of the Favositida.

The type, then, of the genus Chatetes, as here restricted, is the C. radians, Fischer, of the Carboniferous of Russia, and the generic diagnosis previously given is founded upon an examination of the structural characters of this form. It has, however, been pointed out by Mr R. Etheridge, jun., and myself (Journ. Linn. Soc., vol. xiii. p. 365, 1877) that the corals known as Alveolites septosa, Flem., and A. depressa, Flem., are generically inseparable from Chatetes radians, Fischer; and we have further described another species (Chatetes hyperboreus), from the Carboniferous rocks of Scotland, as possessing similar generic characters. All the forms just mentioned are of Carboniferous age, and there are no published species of corals from either older or younger deposits which can, in the meanwhile, be certainly asserted to belong to the same genus. I may say, however, that I have collected in the Devonian Limestone of Gerolstein, in the Eifel, specimens of a coral which would appear to be congeneric with C. radians, Fischer.

If we take the corals just mentioned as the only satisfactorily identified species of Chatetes, we find that the corallum is massive and usually irregularly hemispherical or pyriform in shape,

rarely (C. hyperboreus, Nich. and Eth., jun.) forming thin flattened expansions, with a concentrically-striated epitheca below. The corallites are irregularly polygonal, and are in complete contact throughout their entire length. Rough fractures (generally, but not always) expose the interior of the tubes; and thin sections, whether transverse or longitudinal (Pl. XII., figs. 4, 4 a, 4 d), show that the walls of contiguous corallites are entirely and undistinguishably amalgamated or fused with one another, the originally duplex character of the partition between neighbouring corallites being in no case recognisable. Though somewhat variable in shape and size, the corallites are indubitably of one kind only, and there is no reason for believing that the corallum consisted of two distinct sets of zoöids. The corallites, further, are not reclined, as in the typical species of Alveolites, Lam., but are erect, in precisely the sense that this term is employed in speaking of the massive coralla of species of Favosites, such as F. Gothlandica, Lam., and its allies. The calices, therefore, though wanting the regularly polygonal form of those of Favosites, are never oblique or semilunar, with one lip more prominent than the other, as is so characteristically the case in Alveolites and its allies. The walls of the corallites seem to be wholly imperforate, and as this conclusion is based upon a minute examination of thin sections as well as of actual specimens, its correctness may be accepted as tolerably certain. This character, therefore, alone is sufficient to separate Chatetes from all the externally similar genera of the Favositidæ. No traces whatever either of lamellar or of spiniform septa can be detected in thin sections or in the specimens themselves (except some obscure longitudinal striæ in C. septosus), and these structures must therefore be considered as wholly wanting. There exists, however, in a certain number of the corallites a curious inward projection of the wall (Pl. XII., figs. 4, 46), which is seen both in typical specimens of C. radians, Fischer, and also in C. hyperboreus, Nich. and Eth., jun., C. (Alveolites) septosus, Flem., and C. (Alveolites) depressus, Flem. In the two last-mentioned

species this inward process was noticed and figured by Edwards