CORALS FROM THE INFERIOR OOLITE. 127 
thickened in the middle, and forming four complete cycla; the secondary ones almost as 
large as those of the first cyelum. Colwmella papillose and well characterised. Pali not 
very thick ; the primary and secondary ones broader than those of the third order. Height 
two lines. Diameter three or four lines. 
The calice was imbedded in extraneous matter in all the specimens of this species 
which we have examined, and it is only of late that we have been able to make transverse 
sections of one of these fossils, and thus to ascertain the existence of the characteristic features 
of the genus Zrochocyathus. The figure 14, represents one of these sections restored, and 
shows that the columella and the paliare disposed in the same way as in the tertiary species 
belonging to the same generical group; but this oolitic fossil differs from all these by the 
appearance of its basis, and may for that reason be placed in a peculiar section of the genus 
which we have recently established under the name of Zrochocyathi liberrimi. Inde- 
pendently of that character, Zrochocyathus Magnevillianus resembles much by its general 
form 7. Harveyanus® and 7. obesus,> but differs from them by the structure of the coste. 
This species was first described by M. Michelin, but very incompletely. M. D’Orbigny 
has placed it in his genus Aplocyathus, which, as we have already stated, is composed of 
our Trochocyathus with a circular calice, and is not, in our opinion, admissible.” 
Trochocyathus Magnevillianus belongs to the jurassic period, and it must be remarked 
that there is only one more well characterised representation of the same genus in the oolitic 
formations, whereas they are common in more recent strata. 7. Michelini, which is 
found in deposits belonging to the same great geological period, is of a subdiscoidal form, 
and its basis is not cicatrized, as in 7. AMagnevillianus ; it has as yet been found only in 
the Great Oolite, and the latter in the Inferior Oolite, but we are inclined to consider it as 
being referable to the same genus, some ill-preserved corals that are of a more ancient date, 
and have been found in the lowest formations of the jurassic group and in the Lias. 
This species has been found at Burton Bradstock in Dorsetshire, by Mr. Walton, and 
at Bridport in the same county, by the Members of the Geological Survey. In France it 
has also been found in the Inferior Oolite, near Bayeux, in Normandy. 
! See our Mémoire sur les Polyp. Palzeoz., &e. 
2 Tab. xi, fig. 4. 
3 Milne Edwards and J. Haime, Monogr. des Turbinolides, Ann. des Se. Nat., s. 3, vol. ix, tab. x, fig. 2. 
+ See Part I, page 65. 
