159 CHAPTER VI. GENERA OF FAVOSITIDÆ—(continued). Genus COLUMNOPORA, Nicholson, 1874. (Geol. Mag., new ser., vol. i. p. 253, fig. 1.) Houghtonia, Rominger, Foss. Cor. of Michigan, p. 17, 1876. Gen. Char.- Corallum massive, forming subhemispherical or pyriform masses, often of considerable size, composed of subpolygonal or subcircular corallites, which radiate from the base, and are for the most part in contact and firmly united by their walls. Septa in the form of marginal ridges, generally about twenty in each corallite. Walls thick, perforated by numerous large, close-set, oval mural pores, arranged in rows between the septal ridges. Tabulæ numerous, generally more or less flexuous, often uniting with one another, complete. No columella and no true cœnenchyma. Obs.-The corallum in this genus is massive, and in general aspect very similar to that of any of the larger species of Favosites, though distinguished from the latter even by a very cursory examination. The corallites are in reality subpolygonal, but the angles of the tubes are more or less rounded off, and they thus become subcircular in form (Pl. VII., fig. 2). The real structure of the corallum can be best investigated by means of transparent sections, though many of its most important features can be studied in the actual specimens. The coral lites are essentially in contact with one another—if not invariably, certainly as a general rule-throughout their entire length; though occasionally limited tubular spaces are left at the point of junction of three or four of the corallites.1 Moreover, thin transverse sections (Pl. VII., fig. 2 a) prove incontrovertibly that the walls of the corallites are firmly amalgamated with one another, the junction between contiguous tubes being marked by a wavy dark line. Occasionally, as just remarked, the sections show a tubular space at the angles of junction of the corallites, and these spaces are definitely circular or oval, and are accompanied by smaller rounded and definite vacuities (Pl. VII., fig. 2 6), which are situated in the substance of the walls themselves. These spaces I regard as being cross-sections of tubes which pass through the thick walls longitudinally, and as being, therefore, of the same nature as the canals which I have described in Pleurodictyum under the name of "intramural canals." Similar tubes occur in the walls of Lyopora, Nich. and Eth. jun.; and though I am uncertain as to their true nature, they are clearly endothecal, and cannot be of the nature of "conenchymal tubes." They are, further, very minute, and only the largest of them would be recognised by the use of a hand-lens upon actual specimens. Vertical sections (Pl. VII., fig. 2 c) entirely confirm the evidence derivable from transverse slices as to the absence of anything which could properly be called cœnenchymal. The walls, as before, are firmly united, and the boundary between contiguous tubes is marked by a sinuous dark line, occasionally interrupted by an irregular or oval space. The septa are best studied in transverse sections (Pl. VII., figs. 2 a and 2 6), though excellently seen in the actual 1 Occasional and partial absence of complete contact between the tubes is by no means an unusual phenomenon in genera in which the corallites are normally and regularly polygonal and accurately contiguous. Thus, in Columnaria (Favistella) alveolata, Goldf., it is not uncommon for the tubes close to their mouths to become, in parts of the corallum, slightly separate, in which case they are also subcircular, though the corallites are ordinarily prismatic and in close contact. In Columnaria (Favistella) calicina, Nich., again, some of the corallites are always more or less disjunct and subcircular, while others are always polygonal and firmly united by their walls. specimens themselves. They have the form of from fifteen to twenty or more longitudinal ridges, which have broad bases, and extend only a very limited distance inwards towards the centre of the visceral chamber. The tabulæ are seen in vertical sections (Pl. VII., fig. 2 c) to be complete and numerous, more or less flexuous, and often uniting to a limited extent with one another. They do not, however, carry this process of anastomosis so far as to give rise to anything like the “subvesicular" tabular tissue of Michelinia. Lastly, the mural pores are seen both in transverse and longitudinal sections, though best in the latter. In transverse sections (Pl. VII., fig. 2 a) they appear as transverse channels crossing the walls, and allowing contiguous tube-cavities to communicate. In vertical sections they are only seen where the plane of the section may happen to coincide with that of one of the walls of the tubes, and then they are seen to have the form and arrangement observable by the ordinary methods of examination in the actual specimens. They appear, namely (Pl. VII., figs. 2 c and 2 d), in the form of numerous longitudinally-placed oval pores of large size, which occupy the interseptal spaces, and place the visceral cavities in direct and free communication. The number of these pores in a given space is not absolutely uniform in all parts of a given specimen; but they are usually placed at much less than their own diameter apart, measured both vertically and laterally, so that the walls become completely cribriform. In his excellent work upon the Fossil Corals of Michigan, Dr Rominger, in 1876, founded the new genus Houghtonia, to include certain corals from the Cincinnati group of North America, which I cannot doubt to be really congeneric with the previously described Columnopora. Indeed, Dr Rominger has himself admitted this identity in a note appended to a later edition of the same work (1877). In his description of the genus Houghtonia, as originally published, and in the note just alluded to, in which he admits that this name must be abandoned in favour of Columnopora, Dr Rominger states that the coral L lites are often separated from one another by an irregular cellular cœnenchyma, and that the walls of the tubes when contiguous are not perforated by mural pores, though he gives no drawings of the structure of the corallum which would support either of these statements. I cannot, of course, offer any opinion as to the phenomena presented by Dr Rominger's specimens, as I have not had any opportunity of examining them, and I should not wish to dogmatise as to examples which have not come under my direct observation. It must be borne in mind, however, that the specimens in my possession are the ones upon which the genus was founded, and that they are therefore the types of the genus. These specimens have been subjected to a careful macroscopic and microscopic examination, and I can confidently affirm that they possess walls of an exaggeratedly perforate type (as compared with Favosites); that their corallites are for the most part indubitably in contact, with their walls absolutely fused with one another; and that any interspaces which may here and there exist between the corallites admit of being explained upon a different supposition than that they are of the nature of "conenchymal tubes." The drawings which I have given, being taken by the camera lucida from microscopic slides, will sufficiently prove the accuracy of these statements. A more difficult point to settle concerns the relations of Columnopora to Calapacia, Billings; and as I have no specimens of the latter, I shall here say the little that is necessary concerning the curious types included by the eminent Canadian palæontologist under the above name : The genus Calapacia was defined by Mr Billings in the 'Canadian Naturalist' (2d ser., vol. ii. p. 425, 1857) as follows: "Corallum composite, forming hemispherical or subspherical colonies. Corallites slender, tubular, perforated as in Favosites, and with their outside striated by imperfectly-developed costæ. Radiating septa (in the species at present known) about twentyfour. Tabule thin, and apparently in some instances not com plete. When the corallites are not in contact, the space between them is filled with a variously-formed vesicular tissue. This genus resembles Heliolites, but differs therefrom in having double the number of septa and the walls perforated." Two species were described by Mr Billings as belonging to this genus-viz., C. Canadensis, from the Black River Limestone, and C. Huronensis, from the Hudson River formation. The former is stated to have corallites about one line in diameter, and generally in contact, although still remaining circular; while the mural pores are arranged in horizontal rows running all round the tube, one row between each pair of tabulæ. The latter was separated specifically from C. Canadensis, principally upon the ground of the greater slenderness of its tubes. Neither of these forms was figured. From the above description it would appear that Calapacia Canadensis and C. Huronensis are corals nearly allied to the form which I have described as Columnopora cribriformis; but such a conclusion has been rendered very hazardous by the publication by Mr Billings, at a later date, of a third species of Calapacia, which was both described and figured (Cat. Sil. Foss. of Anticosti, p. 32, fig. 15, 1866). The species in question (viz., C. Anticostiensis) is stated to have a hemispheric corallum, the corallites sometimes in contact, but usually distant from one another by a quarter or half a line. The shape of the corallites is circular, and they are surrounded on the exterior by a fringe of welldeveloped costa, while the spaces between them are subdivided by horizontal and close-set exothecal plates. The septa have the form of longitudinal striæ, and tabulæ were only obscurely seen. In a note Mr Billings adds that this species would seem to be congeneric with Syringophyllum organum. Whether or not Mr Billings be correct in the suggestion just alluded to, the above description and the figures which accompany it leave no doubt whatever as to the entire distinctness of Calapacia Anticostiensis, Bill., and Columnopora cribriformis, Nich. If, therefore, the originally-described species-viz., Calapacia Canadensis and C. Huronensis-are to be regarded as |