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 cyclum. Columella papillose and well characterised. Fall 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 Trochoci/athus, The figure \b, represents one of these sections restored, and 

 shows that the columella and the pali are disposed in the same way as in the tertiary species 

 belonging to the same generical group ; but this oolitic fossil difi'ers 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 TrochocT/athi liberrimi} Inde- 

 pendently of that character, Trocliocyatlius Magnemllianus resembles much by its general 

 form T. Harveyanu^^ and T. obcsus,^ but differs from them by the structure of the costse. 



This species was first described by M. Michelin, but very incompletely. M. D'Orbigny 

 has placed it in his genus Jj^loci/athus, 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. T. 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 T. Maynevillianus ; 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 jiurassic 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 Memoire sur les Polyp. Palseoz., &c. 



2 Tab. xi, fig. 4. 



^ Milne Edwards and J. liaime, Monogr. des Turbinolides, Ann. des Sc. IN'at., s. 3, vol. ix, tab. \, fig. 2. 



* See Part I, page Go. 



