CORALS OF THE CRAG. 5 
cicatrized, and becomes rounded, at the same time that it expands laterally, as does the 
rest of the corallum, which ceases to be cylindrical, and assumes a compressed form 
(figs. ly and 1%). Soon after the peduncle begins to become thin, and to shorten (fig. 1?) ; 
the absorption continues till it disappears completely, and the under edge of the corallum 
becomes long and obtuse. While these modifications are going on, other changes are 
produced in the internal structure of the corallum. As soon as the tertiary septa appear, 
the columella begins to rise, and the primary and the secondary septa, which have become 
rather broad, give off some spiniform trabicule, that unite with the columella. The 
simultaneous development of the twelve tertiary coste also determines considerable change 
im the general form of the corallum; the calice, instead of being horizontal, becomes 
arched (figs. 1y, 14, 12), and the sides of the wall corresponding to the long axis of the calice 
not having yet expanded towards the basis, the corallum has the form of a small battledore ; 
but when the tertiary costa increase in size, the convexity of the calice diminishes, and 
the base of the corallum spreads out, till it assumes the form of a broad, obtuse wedge 
(figs. 1, 1a), which it retains in the adult state. 
The Sphenotrochus intermedius is easily distinguished from Sphenotrochus crispus, 
S. miatus, S. pulchellus, S. granulosus, and S. semigranosus (species which all belong to the 
Eocene period), by the costee being smooth, and not formed by a series of large granules. It 
resembles 8. granulosus by its general form, and 8. crispus by its calice. We are acquainted 
with only three other species, which have also smooth cost, and have often been confounded 
with S. intermedius. One of these leevicostate species is the S. Andrewianus, which lives 
on the coasts of Cornwall and of the Isle of Arran, but is easily distinguished by its narrow 
subconical base, and the slight elongation of its calice, the two diameters of which are as 
100: 120. The second levicostate species, which we designate by the name of Spheno- 
trochus Remeri,' differs also from S. intermedius by its narrow base. The third species, 
S. Milletianus, bears great resemblance to the latter, and belongs to strata occupying the 
same geological formation, a circumstance that has also contributed to create confusion 
between them. But the 8. A/i//etianus found im the Faluns of Anjou is characterised by 
its lateral costae being much less prominent, and its base being more rounded and less 
compressed than in the S. intermedius. 
This fossil is common in the Coralline Crag, and the Red Crag at Sutton. We have 
ascertained its identity with the species found in the Crag of Antwerp, by comparing it 
with the specimens belonging to the collection of M. H. Nyst, at Louvain, and with that 
of Goldfuss, in the Poppelsdorf Museum, at Bonn. Specimens of this species exist in the 
1 This undescribed species has most of the characters of S. mivtus, but the coste are all similar and 
smooth. The lateral ones are not notably larger than the others, and those adjacent are slightly curved 
near their lower end, and sometimes interrupted. The primary and secondary septa are equal, and those 
of the third cyclum are narrow ; all are thick towards the outer edge, and but slightly granulate. Calice 
twice as long as itis broad. Length two lines; breadth one line and a half; thickness one line. A fossil 
of the Miocene strata of Cassel and Hildesheim, belonging to the Museum of Bonn. M. Nyst possesses a 
specimen of the same species found in the Crag of Antwerp. 
