290 DESCRIPTION OF CHALK CORALS. 
in perfect exteriors presented a continuous layer, indicative, it was conceived, of 
the branch having attained its full lateral development. The abnormal fragments 
(fig. 8h) gave a seeming greater distance between the apertures, but the intervals 
were traversed by straight ridges, which often united so as to form a polygonal 
figure, and they were believed to be the boundaries of tubes still more defective 
than those immediately adjacent with a circular outline, though the latter had 
evidently never attained a mature condition. The internal composition of the 
coral is exhibited in figure 8 f, which shows a considerable downward extension 
of the tubes with a gradual decrease in width. The cavities preserved however 
a round periphery throughout, though the interspaces were narrow ; and the 
latter exhibited no signs of a separating fissure, or indications that a partition 
could be effected mechanically. Connected with some apertures was a long 
channel which ranged upwards along the surface of the branch, and was bounded 
on each side by a ridge (fig. 8g). No case of an outer covering was observed, 
but as the channels occupied the position of ovarian capsules, it was conjectured 
that they might have performed the functions of those vesicles. ‘The specimens 
examined afforded no satisfactory evidence of regular surface-thickenings, never- 
theless as they consisted wholly of detached branches, without the least portion 
of a base, a progressive external alteration may be one of the characters of the fossil. 
Tab. XVIII. A. figs. 9& 9ato9g. 
Three figured corals exhibit characters somewhat analogous to those of the 
zoophyte about to be noticed :—1. the fossil referred by Faujas de St. Fond to 
the genus Flustra, and represented in plate 39, figures | a, 1 6 of his work on 
Maestricht ; 2. the Retepora clathrata of Goldfuss (Petref. tab. 9. f. 12), also from 
that locality ; and 3. the Apsendesia dianthus of M. De Blainville (Man. d’Actinol. 
pl. 69. f.2)'. Respecting the first of these generic determinations no remarks are 
necessary ; with regard to the second, M. Milne-Edwards says, ‘‘ nous doutons 
beaucoup que cette espéce soit un Retepore’;”’ and the English chalk fossil most 
assuredly is not a Retepora ; the third genus, Apsendesia, has not been described in 
sufficient detail to admit of its characters being fully understood ; but on account 
of M. Michelin’s careful delineations of Aps. dianthus, it is necessary to institute 
a comparison between the figured species and the ascertained structures of Mr. 
Dixon’s coral. The genus was proposed by M. Lamouroux®, amended by M. 
* Consult M. Michelin, Icon. Zoophytol. pl. 55. fig. 4a, 6, ec, for more precise delineations, parti- 
cularly fig. 4. 
> Lamarck, edit. 1836, t. ii. p. 282. ’ Exp. Méthod. p. 81-82. tab. 80. figs. 12, 13, 14. 
