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ON A NEW SPECIES OF DIASERIS.
BY THE REV. J. E. TENISON-WOODS, F.G.S., F.L.S., PRES. LINN. SOC. N.S.W.
Amongst some corals recently dredged at Port Denison by Messrs. Haswell and Morton there is one new species of a very interesting character. It belongs to the section Madreporaria aporosa, family Fongidoe, second sub-Family Lophoserinoe. Amongst the simple and free corals of this division there is one with bare and lobed walls which Messrs. M. Edwards and Haime experienced much difficulty in assigning to any position because of the incomplete character of the calice. A new genus was erected for it, placed as above, removing it from the genus Fungia in which it had been included by Michelin (Magasin de Zoologie, Vol. V., 1843).
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The genus is thus described:- "Diaseris. Corallum simple, free, discoid, with a bare and costulate wall with a structure similar to Cycloseris, but in its young state it is formed of a certain number of separate petaliform lobes which in the more mature state become more or less united by their edges." The authors add that in all the various families of corals no other instance of this structure is known. Two species wore described by them, Diaseris distorta, Michelin, of unknown habitat and D. Freycineti. Both were large, viz., 50 millimetres across and 10 high, and the differences between the species were that D. Freycineti was a coral with closer septa which were not so high as D. distorta. See Hist. Nat. des Corallaires, Vol. III., p. 54. Also Comptes Rendus de l'Academie des Sc., Vol. XXIX., 1849, p. 72.
The species to which I have now to call attention is very much smaller than either of the preceding and there are also peculiarities in the septa as I shall proceed to show.
DIASERIS MORTONI, n.s., Plate XV., fig. 1, 2. [Plate not currently included]
Corallum semicircular, thin, subdiscoid, divided into two, three or four lobes in some specimens, though the majority are completely semicircular with an entire rounded edge. Base flat or concave in the slightest degree, showing no trace of any former separation between the lobes. Costa distinct, fine, granular and corresponding with the septa, but all equal in thickness and taking their origin from the edge at distances the same at the various orders; the outer edge of the septa projecting like the teeth of a fine cog-wheel outside the base. In nearly all the specimens these were four distinct systems, though some had only three, two, and some with only one and the rudiments of two others. The cycles depended on the age of the specimens. They ranged from five to eight incomplete. All aro granular, but the granules are in ridges so as to give rise to a vermicular surface and the ridges project at exactly opposite sides of the septa; the
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synapticulae are few and quite at the base. The primaries are quite free with a conspicuous thickening at their origin ; the secondaries are also free with a slight thickening, and both have a rounded crenulate margin. All the other orders gradually branch out or divaricate from one another with a gradual curve. They are very incompletely formed so as to be deeply divided into irregular paliform lobes. The height to which the septa rise is also dependant on their age, the first being much higher than the rest and sloping gradually from the margin upwards towards the central fossa and so on proportionately for all the cycles. All except the central septum curve towards the outer margin so as to preserve a flabellate form. In the fossa there are a few papillae of a columella.
There can be no doubt that this form of coral is a form of Cycloseris, in which some of the systems are aborted. In this view there is nothing to distinguish the present species from C. cyclolites except the size. I do not say that this is the true nature of the organism, but a close attention to the young stages will reveal the whole matter. It will be observed that one strong point in favour of the explanation which is suggested for this abnormal coral is the variation in the number of systems which are aborted. In many instances all are gone but one. In this case however, we have a semicircular fringe of septa round the fossa which represents all the other systems. Another fact is the occurrence of one or two specimens in which only one system is aborted. In this case the coral is to all intents and purposes a very small and depressed C. cyclolites minus one system.
About sixty specimens were dredged up off Holborn Island. They are of various sizes and seem to indicate some disadvantageous circumstances in their growth by which they have been stunted. Some of the specimens were much eroded and full of small grains of sand, foraminifera, &c. I have dedicated the species provisionally to Mr. Alexander Morton.