270 DESCRIPTION OF CHALK CORALS. 
the inequalities of the subjacent body, but some could not. Where most uni- 
form, the surface of the tubes was rounded (a, b), and the sides nearly straight 
or parallel ; occasionally however hemispherical swellings with curved sides 
occurred, and were evidently due to the tube passing over one of the larger 
papille of the Echinoderm. The distance between successive apertures was 
sometimes also considerably shortened, without any compensating lateral expan- 
sion of the tube, indicating, it is presumed, imperfect development. Such ir- 
regularities as those exhibited by figures 1* and 1 ¢ clearly originated in causes 
totally independent of the nature of the subsurface, and were conceived to have 
arisen from the accidental association of many ova. 
The most decided bifurcations gave two tubes issuing from the extremity of 
the parent, and diverging more or less symmetrically ; but so far as the speci- 
men examined was concerned, there was much less constancy of character in this 
respect than in M. Edwards’s enlarged figure 2a, a branch springing often at 
right angles from the proximal extremity of a tube, or even from the side; but 
the former at least are possibly only abnormal conditions influenced by local 
interferences. Occasionally the two branches ranged for a short distance paral- 
lel to each other and in close contact, and then diverged or one of them perished. 
An instance of this mode of growth is shown in M. Edwards’s figure 2a; and 
the apparent biserial apertures were referable to it. The mouths were generally 
oval, the greater diameter being in the direction of the tube ; and the best-pre- 
served were not mere tubular extremities, but in the plane of the general surface, 
with more or less of contraction: the margin, where retained, was thickened and 
slightly raised. The alternate inclination to the right and left was often very 
marked ; but it is necessary to state, as a distinction from M. Milne-Edwards’s 
genus Criserpia’, that the arrangement did not arise from the tubes issuing late- 
rally. Figure 2 a of the ‘ Annales des Sciences Naturelles’ represents frequently 
an enlargement in the region of the apertures with a somewhat pear-shaped out- 
line ; nothing similar was detected in the English coral, and the discrepancy was 
most probably not an essential, but an accidental difference. The base or at- 
tached lamina of the tubes was very thin, scarcely concealing the papille of the 
Micraster, while the outer wall was thick and solid and transversely rugose. 
No doubt was entertained that the coral represented by figure 1 c, and which 
was situated close to the specimen partly given in figure 1 a, was an example of 
irregular production of Alecto gracilis, every portion displaying the strongest 
' Ann. Se. Nat. 2nde série, Zool. t. ix. or Recherches sur les Polypes, Mem. sur les Crisies, &c. p. 16. 
