CORALS FROM TUE PERSIAN GULF. 1027 



open, deep. Septa in four conplete cycles. Primaries large, very 

 prominently exsert ; quaternaries join over the tertiaries, and again 

 deep down in the calice over the secondaries; quaternaries on either 

 side of the primaries much developed, and prominently exsert in 

 the manner typical of the genus lleterocyathus ; all septa beset with 

 numerous fine granulations arranged in radial ridges. Pali in the 

 form of small denticulations, which pass imperceptibly into a 

 parietal, fasciculate, centrally depressed columella. At the base, a 

 circular aperture leads to an ^sp!(rZosi/;»Ao;i chamber containing a 

 small Gastropod shell, in which a Sipunculid lives commensally 

 with the coral zoophyte. 



Nine specimens. 



Locality, Karachi. Depth 15-40 fms. ; bottom, shell-sand. 



Paracyathus cavatus Alcock [1]. (PI, LVII. fig, 5.) 



Corallum simple, fixed by spreading base and expanding slightly 

 to lip of caiice. Height varies between 15 mm. and 20 nun., but 

 the shortest has the largest calice. Calice variable in shape, 

 probably owing to local surroundings ; in some specimens calice is 

 circular, in others oval, while others have various indentations 

 and excrescences. Diameters of calices 15x15 mm., 16x12 mm., 

 17 x10 mm., 18x15 mm., 20 x 13 mm., 20 x 18 mm. Costte visible 

 from base upwards, low broad ridges covered with minute 

 granulations, corresponding to each septum ; towards the lip of 

 the calice these costal ridges become more marked, and somewhat 

 stouter and more exsert costaj alternate with slightly smaller 

 costte. This alternation of larger and smaller costa; is apparent 

 in some specimens at the extreme base of the corallum as well as 

 at the calicular margin. Septa close, not markedly exsert ; the 

 size of the septa and the extent to which they are exsert 

 diminish in a descending order of magnitude according to the 

 cycle to which they belong : those of the first cycle are larger 

 than those of the second, the second than the third, and so on. 

 They are uniformly covered with minute granulations, which are 

 arranged in a series of longitudinal and radial rows. The calice 

 is widely open, and the inner margins of the septa are cut up 

 into large irregular nodules representing small pali, which pass 

 imperceptibly into a fasciculate parietal, centrally depressed 

 columella. There appear to be typically five orders of septa, but 

 those of the lower orders are not always easy to interpret. The 

 primaries are always large and extend to the columella; their 

 paliform nodules are slightly larger and more projecting than those 

 of the septa of lower orders ; the septa of lower orders tend to fuse 

 together near the columella, and pass into it as an ill-defined mass 

 of minute pali. The larger size of the primary septa and the 

 grouping together of those of other orders give a hexagonal 

 starlike effect to the calice. In none of the seven specimens from 

 the Persian Gulf are the five cycles complete, although in one 

 there are 94 septa, only two septa of the fifth cycle being missino-. 

 In the specimen figured (text-fig. 217), however, there are also 



