Dekayia ulrichi

• Zoarium Morphology:
• Zoecia:
• Mesozooids:
• Monticules: Broadly rounded. Situated along the organism approximately 3 millimeters from one another.
• Maculae:

• “Corallum ramose, branches from 1.5 to 3 lines in diameter, cylindrical or subcylindrical, often irregularly swollen at intervals, dividing dichotomously usually at considerable intervals. Corallites with moderately thick walls the average ones of unequal sizes about eight in the space of 1 line, and having very minute tubuli sparingly interspersed amongst them. Surface smooth, destitute of tubercles, but occasionally showing groups of corallites which are very slightly larger than the average.
• “The examples of this species which I possess from the Clinton group Upper Silurian agrees entirely with the description given by Edwards and Haime, being smooth, and simply having moderate numbers of very minute tubes irregularly intercalated amongst the ordinary corallites, these latter varying slightly in their dimensions. On the other hand, the Lower Silurian examples which I have referred to this species, though also smooth, and also having minute tubuli sparsely interspersed amongst the larger corallites, exhibit distinct groups of corallites which are of rather larger size than the average, and which are not set upon distinct elevations. They thus approach C. pulchellus, from which they are hardly distinguishable except by the fact that the group’s large sized corallites are not nearly so conspicuous, the individual corallites which compose them being only very slightly above the average size. On the contrary, in C. pulchellus the groups of large-size corallites are very conspicuous, as the corallites composing them are nearly or quite twice as large as the ordinary ones. Perhaps the Lower-Silurian forms here regarded as referable C. fletcheri may constitute a distinct variety either of this or C. pulchellus” – Nicholson loc. cit.
• As is well known now this species is not the same as the Silurian Chaetetes fletcheri, under which name Nicholson described it, as he himself pointed out (Genus Monticulipora, p. 131) when he came to investigate the internal characters.
• Its external characters are indicated above, with the exception that a very abundant series of mesopores is usually developed, the zooecia are ring-like, and the acanthopores frequently in well preserved material give rise to minute spines at the surface. The zoaria are characteristically smooth and cylindrical, and medium size, the specimen figured (after Nicholson) being about typical. As to internal characters, in tangential sections the mature region, the zooecia are seen to be nearly always circular, with moderately thick walls, and surrounded by small angular mesopores. Scattered among the zooecia and imbedded in their walls are a moderate number of acanthopores of two sizes, the greater number being small and not conspicuous, while are occasional much larger ones, that seem to arise much in the zoarium than the smaller ones, the latter being confined the mature region. In longitudinal sections the zooecia and mesopores are both seen to be crossed by well defined and complete diaphragms, rather more crowded in the mesopores. These are much less frequent in the axial region. The zooecia bend rather abruptly from the axial into the mature region, and emerge at right angles to the surface, where their walls become considerably thickened.

Cumings (1902):

• In the case of Dekayia ulrichi, I believe we are dealing with an incipient genus. This species has a considerable range and distribution and is highly variable. It varies from strictly ramose to strictly frondescent (var. lobata); from perfectly smooth to monticulose (D. robusta); from very small and delicate (D. obscura), to robust and submassive (D. robusta). In internal structure the zooecia may be thick-walled or comparatively thin-walled; mesopores are usually numerous, but may be considerably reduced in number. The tabulation varies but little, and the wall structure is always essentially the same.
• I have shown that the smooth type of Dekayia ulrichi produces in the Lorraine a truly frondescent form. The monticulose type (D. ulrichi-robusta) also produces a frondescent form that ranges throughout the Lorraine. This is the D. ulrichi-expansa of the above list.

Foord (1884):

• Corallum ramose, frequently branching. Branches thick, usually cylindrical, sometimes compressed. Surface covered with small but tolerably conspicuous monticules, situated about 3 millimetres apart, and bearing cells of a somewhat larger size than those in the intermediate spaces. The apertures of the corallites are polygonal in outline, and in places where the surface is well preserved some of the larger of the spiniform corallites may be seen with a hand lens. Of the larger corallites about four occupy the space of 1 millimetre, of the smaller about five.
• Microscopic characters. – Tangential sections reveal clearly the dimorphic character of the corallum, which is provided with two kinds of tubes, large and small; both are of polygonal form, and their outline is inflated in many places by the occurrence of numerous spiniform corallites. These also are of two kinds: The larger are usually situated at the angles formed by the junction of four or five cells, and fill a space quite as great as that occupied by some of the interstitial cells; the smaller are generally found to be in the substance of the cell-walls, about midway between two angles. The spiniform corallites form a very conspicuous feature in tangential sections of this species, and give to such sections a highly characteristic appearance. Under a moderately high power traces of the original walls of the corallites may be discerned in tangential sections; but as a rule this structure appears to have been destroyed in the process of fossilization. In longitudinal sections the two sets of tubes are clearly brought into view. In the larger ones there are numerous horizontal, sometimes slightly oblique, tabulae, situated at from one-half to one tube-diameter apart; they begin in the axial region of the corallum, and are about equally developed in their course from thence to the peripheral region. The smaller tubes do not differ in the character of their tabulation from the larger ones, except that the tabulae in the former are a little more frequent than they are in the latter. There is a feature worthy of note in the structure of the walls of this species, and that is a periodic inflation, which reminds the observer of a similar structure characteristic of the genus Stenopora (Lonsdale). Mr. Ulrich draws attention to a like feature in his description of a Cincinnati-group species of Dekayella – D. obscura Ulrich (Journ. Cincinnati Soc. Nat. Hist. vol. vi, p. 150).
• On leaving the axial region the tubes rapidly thicken towards the surface, the spiniform corallites being seen at frequent intervals piercing the corallum and intermingling with the ordinary corallites. The spiniform corallites appear to originate in the axial region of the corallum, as they may be seen in sections cut as deeply as it is possible to make them without destroying the walls of the tubes.
• It may be well here to enumerate the chief characters which separate this species from the only two known to the writer, viz.: Dekayella ulrichi, Nicholson, and D. obscura, Ulrich – both from the Cincinnati Group of Ohio. From the former of these the present type may be distinguished as follows: – by its much more robust habit of growth, by the possession of monticules, and by the much greater number of its tabulae and spiniform corallites. The exceedingly small and delicate corallum of D. obscura, Ulrich, would be sufficient alone to differentiate it from D. robusta, and added to this the great development of the tabulae and spiniform corallites in the latter make the distinction between the two forms sufficiently clear.

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