32 
PROFESSOR P. M. DUNCAN ON THE STRUCTURE 
duced in this paper a notice of the species of the Secondary rocks which were known 
to depart from the usual hexameral type, and which were described by MM. Milne- 
Edwards and Jules Haime* and by M. de FROMENTELf. This course of proceeding 
is necessary in order to show how the rugose type has persisted during the Neozoic ages. 
II. Genus Guynia. 
The corallum is simple and long. The wall is thick and solid. The septa are well 
developed, lamellar, unequal, and are continuous from the base to the calice. There 
are four systems of septa, and one primary septum is longer and larger than the others. 
The columella is essential, and is attached to the larger septa. There is no endotheca. 
The costse are visible on the growth-rings of the outside of the wall. There is an 
epitheca. 
Species Guynia annulata, sp. nov. Plate I. figs. 1-8. 
The corallum is long, cylindrical, and narrow ; it is sometimes curved. The accretion- 
ridges are well developed and regular, and are marked with prominent short spinules, 
laminae, or granules which correspond with the costse. The epitheca ornaments the 
ridges, and is delicate. The costse extend over the whole length of the corallum, and 
usually exist as flat bands between the close and rather wavy accretion-ridges. 
There are four principal septa, one of which is larger than the others at the calice. 
The four secondary septa are often as large as the primary, but the eight tertiary septa 
are almost rudimentary. There are four systems of septa, and three cycles in each ; none 
are exsert. The columella is stout, cylindrical, deeply seated in the calice, and adherent 
to the larger septa. The interseptal loculi are large, and the transverse outline of the 
corallum is sometimes rather angular. The length of the perfect corallum probably 
f- inch, the breadth ^ inch. 
Locality. Adventure Bank in 92 fathoms. 
The numerous specimens of this coral are in excellent preservation, and their condition 
is that of living forms whose soft parts have been crushed or washed out during the 
operation of removal from their usual locality. Many of the corals adhered by their 
sides to mollusca, and resembled annelid-tubes marked with a regular series of ring-like 
accretion-ridges. 
III. The numerous growth-rings or accretion-ridges give the species a very palaeozoic 
facies, especially when there is a very decided constriction between two annular promi- 
nences : this facies is made more decided when the tetrameral arrangement or type of 
the septa is noticed and the solid columella is distinguished. The stout wall and the 
absence of endotheca are exceptional peculiarities ; but although they are not mentioned 
in the diagnosis of the Rugosa by MM. Milne-Edwards and Jules Haime, they are 
admitted as characterizing a most important family of them — the Cyathaxonidce. 
* Hist. Nat. des Coralliaires, 1860. 
f E. de Fromentel, ‘Polypiers fossiles,’ 1858-61. 
