154 DESCRIPTION OF CORALS. 
English fossil would forbid all thought of identifying the two corals with each 
other. Referring in the next place to M. Michelin’s figure of the same species 
(Idm. coronopus, Icon. Zooph. pl. 46. f. 16), the dorsal surface will be found to be 
round as well as the oral, giving to the lower portion of the specimen in part not 
a triangular, but an oval outline ; the innermost tubes of the transverse rows are 
also so disposed as to constitute a medial or longitudinal series of apertures, 
and might be considered as ‘‘ une sorte de créte.”” In the mode of branching, the 
specimens delineated by Dr. M.-Edwards (loc. cit. f. 3. nat. size) and M. Michelin 
(loc. cit. f. 16) agree almost perfectly, the offshoots springing uniformly from 
one and the same side; and they differ therefore, to the extent exhibited, 
markedly from the English fossil, in which the amount of divergence to the 
right and left is equal at each bifurcation, and in accordance with M. Edwards’s 
magnified figure 3a. An examination, however, of tolerably large specimens 
of the nearly allied genus, Hornera, will prove that in corals of this family 
the mode of branching cannot be adopted as a specific distinction (consult 
‘ Mém. sur les Crisies,’ &c. pl. 9.f. 1). It must farther be stated that Dr. Milne- 
Edwards, in his description of Idm. coronopus, assigns to it the Grignon fossil, 
regarded by M. De France as a variety of the Idm. triquetra of Lamouroux (Expos. 
Méthodique, p. 80. pl. 79. f. 13-15), an oolitic species. If the figures of the 
tertiary coral given in the Atlas to the ‘ Dictionnaire des Sciences Naturelles’ 
(Polyp. pl. 46. f. 2), or in the ‘ Manuel d’Actinologie’ (pl. 68. f. 2), be con- 
sulted, additional varieties of structure will be found, as well as of growth. 
Respecting Idm. gradata, the other Paris basin species, it is perhaps sufficient 
to state that Dr. Milne-Edwards was inclined (1838) to consider it also as only 
a variety of Idm. coronopus, but without having examined specimens, and that it 
has not yet been noticed by M. Michelin. 
The foregoing allusions to differences in published figures have not been made 
to raise a doubt respecting the correctness of the determinations ; on the con- 
trary, it is believed that the fossils thus represented may all be referred to one 
species, exhibiting merely different conditions of growth or of outline, due to 
progressive thickening of the branches ; and the want of perfect accordance has 
been noticed chiefly to justify the doubtful assignment to the same species of the 
Bracklesham coral. 
Fig. 24. Tab. EX. displays fully the general mode of growth of the English spe- 
cimen, and the divergence from a centre was even more marked before a branch 
was detached from one of the intervals to obtain a cellular surface. The spe- 
