272 DESCRIPTION OF CHALK CORALS. 
or more repetitions of the same process. The specimen itself exhibited three 
instances of two young circular crusts on a disk, with examples of others on its 
very margin, and the latter would clearly have enlarged the superficies still more 
had they attained their full growth. That the added centres did not originate in 
germs ejected from pre-existing tubes, but from the general polype-substance, 
may be inferred from the characters of other ascidian zoophytes. The genus 
Lichenopora’ sometimes presents a single disk, and sometimes according to M. 
Michelin an aggregation of disks, as his Lich. cumulata*, L. conjuncta®, and L. 
tuberosa*, and it would be difficult to imagine how the two last, at least, could 
owe their many-centred composition except to a reproductiveness in certain por- 
tions of the polype, not limiting the term to the viscera and appendages sur- 
rounding the mouth. Further examples may be noticed in the Ceriopora dia- 
dema*® and Cer. stellata’ of Prof. Goldfuss, also in M. Michelin’s Cer. papularia’ : 
it is likewise hoped that the reader will find proofs of such productive operations 
in the fossil to which in a subsequent page is applied the term Atagma. 
The only specimen examined was about 1{ inch in length by 8 to 9 lines in 
breadth, and it consisted of about eleven united disks, including those along the 
boundary, and of which only portions had been preserved. The whole formed an 
irregular but continuous layer, which had evidently coated an uneven perishable 
body. The greatest diameter of the disks was about 3 lines, the form being 
generally polygonal from mutual interference ; and the margin was occasionally 
a narrow smooth band, in which could be detected the outline of tubes that 
had never attained a perfect development, no traces of a mouth being per- 
ceptible ; but very frequently there was.a crest-like intermingling of perfected 
visceral cavities. The outer surface of the tubes, where visible, was rounded or 
flat; and the exposed portion varied with the nature of the surface or its in- 
equalities, amounting in some cases to fully half a line; while often successive 
apertures were in contact. The mouths were simple tubular apertures, with or 
without a slight contraction ; but they were often wholly closed by polype secre- 
tions similar to those which coated the general surface, and concealed more or 
less the range of tubes that would otherwise be visible ; and even in a few places 
leaving but faint indications of their existence. 
' De France, Dict. des Se. Nat. tome xxvi. p. 257. 
SOpucrtnplaumitien tele = 1b (68 1 IGE * Pl. 14. f. 6. 
> Petref. pl. 37. f. 3, not pl. 11. f. 12, identified by M. Michelin with his Lich. conjuncta, Icon. 
Zoophy. p. 277. ® Petref. pl. 30. fig. 12. 
? Op. cit. pl. 32- f.7; consult also M. Michelin’s Cer. Landriotit, pl. 1. fig. 10. 
