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 

 Astrangiaceee be comprehended. 



TURBINOLID^E REPTANTES. 



Corals rising from a prolongation of the basal structures, some- 

 times distant, sometimes very close. The septa are plain ; and there 

 is no endotheca. 



This diagnosis forms a group amongst the Turbinolidae 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 oc- 

 casionally assume this basal method of growth. I believe " occa- 

 sional" is a correct term, and that the force of circumstances which 

 prevent the upward growth, and necessitate a basal one, is accom- 

 panied 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 Polycyatiius. 



There is an epitheca covering the costae ; pali are present ; and 

 the columella is usually deeply seated. 



Polycyathus atlanticus, sp.n. (Plate XXXVIII. 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 ar- 

 ranged ; 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 in- 

 cised 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 costae 

 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 j % -q inch. Breadth of calice A> inch. 



On an Ostrea from St. Helena. 



