58 BRITISH FOSSIL CORALS. 



The septa are small, thin, wavy, unequal, and have very long and sharp lateral spines. 

 The septa are in six systems, but the four cycles are incomplete. The four cycles are 

 complete in two systems, but are incomplete in one of the halves of each of the other 

 systems. There are therefore eight septa in two systems and six in the rest. 



The columella is small and situated deeply. 



The pali arc small, and are situated before all the septa, except those of the 

 last cycle. 



The costge are subequal, broad, very slightly roimded, and barely prominent ; they 

 are generally marked by three rows of granules, and at the calicular margin they become 

 conical, and ornamented with a prominent and wavy ridge-like process, which passes 

 downwards, becoming soon lost in a faint fissure, which may be seen on most of the 

 costse low down. 



Height, ^ths inch. Great diameter of calice, ^ inch. Small diameter of calice, between 

 fijths and ^^ths inch. 



This species is readily distinguished from all other striated Trochocyailii by its shape, 

 septal arrangement, small pah, and the curious ornamentation of the costae. 



Locallti/. Whetstone (Loudon Clay). 



In the collection of N. T. Wetherell, Esq., F.G.S. 



These are the only Trochocyathi which are known in the London Clay, and it is very 

 doubtful if Trochocyathm sinuosus, Brongniart, sp., was ever found there.^ 



Genus — Paracyathus. 

 1. Paracyathus cylindricus, Duncan. Plate IX, figs. 18 — 21. 



The corallum is cylindrical, straight, tall, and has a flat base, whose diameter is nearly 

 equal to that of the corallum. There is a constriction just above the base, the wall is 

 often marked with growth-rings, and in some corallites the calice is slightly expanded. 



The calice is circular in outline, its fossa is shallow, and the columella very small. 



The septa are slightly exsert, and in some calices more so than in others ; they are 

 delicate, are marked with large granules laterally (fig. 21), and have an irregular upper 

 margin. 



There are six systems of septa, and three perfect cycles ; moreover, in one half of four 

 or more systems a septum of the fourth cycle is developed. The septal number is there- 

 fore very irregular, and there are from twenty-eight to thirty septa in the calice. The 



^ See 'Corals of tlie London Clay,' MM. Edwards and J. Ilainie, page 22. 



