320 DESCRIPTION OF CHALK CORALS. 
fossil exists. When a Flustra is composed of opposite strata of cells, a separation, 
as is well known, can be effected mechanically ; but among existing Eschare and 
extinct species generally’ no division with a smooth surface can be made: one 
of the distinguishing characters between the two genera has moreover been stated 
to be a want of agreement, as respects position, in one case, and an agreement 
in the other. In Eschara foliacea, however, when the examination was suffi- 
ciently extended, numerous deviations occurred ; and they could not be regarded 
as merely exceptions®. On instituting a comparison between the structures just 
mentioned and those of the cretaceous fossil, it will appear, that the resemblance 
is with Eschara in one particular, the opposite layers not being separable with 
smooth dorsal surfaces ; while in the total want of conformity in the situation of 
the cells the greatest agreement is with Flustra. So far as the original composition 
could be inferred from the mineralized state, it seemed to have been much more 
calcareous than among Flustre, and the parietes to be considerably thicker. 
The ovarian capsules of the fossil under consideration were well and abundantly 
exhibited (fig. 9 a), being situated at the distal extremity, resting also partly on 
the next cell and blending with it, but the forepart in perfectly preserved ex- 
amples so projected over the mouth of the cell to which it belonged, that that 
aperture was totally concealed, when the general surface was viewed perpendicu- 
larly. In Flustra foliacea, usually regarded as the type of the genus, the capsule 
is similarly placed, but is more crescent-shaped, and its opening (in dried speci- 
mens) is sufficiently inclined backward to permit the free egress of the tentacula, 
if they existed ; and Dr. Grant? in his elaborate memoir states, that when the 
ovum has escaped from the cell ‘‘ a new polype ” is produced within the cavity. 
It would therefore follow that either a portion of the capsule in the fossil was 
displaced, or the viscera and tentacula were not renewed, provided they had 
ever been developed. The blending of the capsule with the surface of the 
next cell indicates its having been formed contemporaneously with the cells ; 
and its highly calcareous nature facilitated the detection of a cicatrice. A few 
instances of such marks were observed, and their limited number proved, it was 
conceived, that only certain cells had been ovigerous. Whether they could ever 
1 For an example of a fossil Hschara, with dorsally divided layers, consult M. Milne-Edwards’s 
memoir, Sur les Eschares Fossiles, Ann. Se. Nat. 2nde sér. Zool. tome vi. pl. 11. f. 8; or Recherches 
sur les Polypes, &c. 
2 Consult M. Edwards’s Mem. op. cit. pl. 9. f.1 e. and pl. 11. f. 8 a. 
% Edinb. New Phil. Journ. vol. iii. p. 841-342. 
