| OCR Text |
Show 1876.] AND LITTORAL CORALS. 433 These observations are necessary, in order that the nature and classification of several corals which closely resemble each other may be understood, and that their separation or not from the Astrangiacese be comprehended. TURBINOLID^E REPTANTES. Corals rising from a prolongation of the basal structures, sometimes distant, sometimes very close. The septa are plain ; and there is no endotheca. This diagnosis forms a group amongst the Turbinolidse like that of the Astrangiacese of the Astreacese ; and this group is as it were linked on to the endothecate corals by the Oculinacese, which occasionally assume this basal method of growth. I believe "occasional" is a correct term, and that the force of circumstances which prevent the upward growth, and necessitate a basal one, is accompanied by trifling changes in the septal arrangement, and in that of the columella also ; so that a species may present itself under two aspects. But until more is known of the soft parts, it is best to make them basal growers when they are only found in that manner. Genus POLYCYATHUS. There is an epitheca covering the costse ; pali are present ; and the columella is usually deeply seated. POLYCYATHUS ATLANTICUS, sp.n. (PlateXXXVIII.figs. 14-16.) The corallites arise close to the bases of their neighbours, and grow more distinct and distant with age. Their shape is cylindro-conical, with a broad base and an elliptical calice, which is circular in outline in young species. The epitheca is very decided in young, and well seen in the old specimens. The septa are irregularly arranged ; and in the largest calices there are four complete cycles and part of a fifth. The primary and secondary septa are the most distinct and exsert, being granular at the sides, but not incised on the margin. The smaller septa do not reach far from the wall. The margin of the calice, round and stout in the young corallite, is rather wavy and even angular in the largest. The costse are subequal, granular, and covered by the epitheca. The columella is deeply seated, small, and ends in a few papillose spines. The pali resemble the spines of the columella, but are usually larger and, indeed, longer than the smaller septa before which they are placed. The pali are placed before the tertiaries and secondaries, those of the tertiaries being nearer the margin of the calice. Sometimes the pali are double or bilobed before these septa, but not before the secondaries. There is no endotheca. Height T% inch. Breadth of calice -^ inch. On an Ostrea from St. Helena. |
