306 DESCRIPTION OF CHALK CORALS. 
of pores; but if in the notice on Atagma its characters are rightly understood, 
no generic identity exists between Cer. papularia and the fossil under consider- 
ation; and the latter is perfectly distinct in every particular from the genus Ce- 
riopora. Under the term Petalopora another zoophyte is described in a prece- 
ding page, as supplied with a secondary series of pores ; those openings however, 
or the canals with which they are connected, penetrate horizontally into the 
branches, and in the general composition of the coral very marked deviations 
from the one forming the subject of the present notice are apparent. Again, in 
an article on some Atherfield zoophytes’, the designation Siphodictyum is applied 
to a Bryozoon which has a large and a small set of pores, but the characters of 
the latter are dissimilar from those of the chalk coral, though the two extinct 
polyparia agree in having the apertures to the visceral cavities on only one sur- 
face of the branches. The compiler of these memoranda is not aware of any 
other published genus of Tubuliporide which possesses an analogous bifold 
structure. Of its existence in many unexamined cases, no doubt can be enter- 
tained ; but wherever it occurs, the properties of the subordinate openings must 
be studied with reference to the interior of the zoophyte, including all the com- 
ponent parts; and in no case can the mere intermingling of large and small 
apertures justify the assigning of a specimen to M. de Blainville’s genus. 
The lateral shoots present characters deemed worthy of attention. These off- 
sets were very numerous, but their growth, both longitudinal and lateral (figs. 3,4), 
depended evidently on the extent of the interspace, for the increase in either 
direction had almost invariably ceased, when a certain proximity had been ob- 
tained, many of the shoots having a conical outline, others an almost lineal form, 
and several were merely rudimentary; and no perfecting of the sides of the 
pinne by the formation of a surface composed wholly of tubuli was observed, 
indicating not only a cessation in the completion of visceral receptacles, but an 
entire limitation of polype development. These peculiarities prevailed in even 
the lowest part of the specimen. Figure 4, which represents a dorsal surface, 
shows longer lateral shoots ; but the intervals are greater, while many similarly 
restricted instances are observable. 
It must be also stated, that changes resulting from age were of a limited 
nature in the specimens examined, the pores remaining open even at the very 
base of the supposed oldest example (fig. 3) ; and the only observed alteration 
being in the intermediate substance. 
* Quarterly Journal of the Geological Society of London, vol. v. p. 90 et seq. 
