Ixiv BRITISH FOSSIL CORALS. 
Sub-order 4. 
ZOANTHARIA RUGOSA. 
Corallum simple or composite, with a septal apparatus never forming six distinct 
systems, as in all the preceding Zoantharia, but appearmg to be derived from four primary 
elements. Sometimes this disposition is rendered manifest by the existence of four well- 
characterised primary septa, or of an equal number of depressions occupying the bottom of 
the calice, and assuming a crucial appearance: in other cases only one of these primary 
septa or excavations is well developed so as to interrupt the radiate form of the system ; and 
in others, again, no trace of septal groups can be discovered, and the whole apparatus is 
represented by numerous equally developed radiate strize rising on the surface of the tabule, 
and extending up the inner side of the walls. The corallites are always perfectly distinct, 
and are never united by means of a ccenenchyma; nor do they ever form linear series, 
which is often the case in the preceding sections. They multiply by gemmation, and the 
reproductive buds are in general developed on the surface of the calices of the parents : 
this often arrests the growth of the latter, and gives rise to a superposition of generations. 
It is also to be noted that the septa, although in general very incomplete, are never porous, 
and never bear synapticule, but that the visceral chamber is in general filled up from the 
bottom by a series of transverse tabulz, or by a vesicular structure, which often constitutes 
the principal part of the corallum. 
Family XII. 
STAURIDA. 
Corallum with well-developed septa, extending without any interruption from the bottom 
to the top of the visceral chamber, united by lamellar dissepiments, and arranged in four 
systems, characterised by an equal number of large primary septa. 
1. Genus STAURTA. 
Corallum composite, massive, astreiform, and increasmg by calicular gemmation. 
Corallites wnited by their walls, or free in part, and not presentmg any costa. Sepia large, 
and with undivided edges, united along the axis of the visceral chamber. No columella. 
Typ. sp., Stauria astreiformis, nob. 
2. Genus Hotocystis. 
Lonsdale, in the Quarterly Journal of the Geol. Soc. of London, vol. v, part i, p. 83, 1849. 
Corallum composite, massive, astreiform, and increasing by extra-calicular gemmation. 
Corallites united by means of well-developed coste. Columella stylitorm. 
Typ. sp., Holocystis elegans ; Cyathophora elegans, Lonsdale, loc. cit., tab. iv, figs. 12, 13, 14, 15. 
