DESCRIPTION OF CHALK CORALS. 283 
obliterated. The component parts consisted, as already stated, of thin lamin or 
ridges and foramina. Inthe youngest condition (fig. 6 a), the former were not con- 
spicuous, but in more advanced stages they formed projecting thread-like ribs, 
which were variously contorted, subdivided and anastomosed, diverging also 
outwardly along the inner face of the cones. They were connected longitudi- 
nally by small transverse bars; and their substance was apparently penetrated 
by very minute pores. The foramina were distributed between the main ridges, 
generally in a single row, and they bore the character of indented punctures 
penetrating horizontally, but were somewhat variable in form and size. In the 
obliterated state their position was indicated by a minute, shallow pit, sometimes 
blended with the transverse bars. A fragment slightly worn down on the front 
presented a reticulated structure resembling that on the original surface, but 
necessarily with a uniformly flat plane, and intersected lateral fasciculi: when 
abraded a little deeper, the longitudinal lines or ribs became indistinct, as well as 
the pores in some places, and the bundles of tubes were exposed to a greater ex- 
tent, penetrating into the body of the branch; while a still deeper wearing (fig. 6 e) 
gave a centre wholly composed of tubes, with diverging fasciculi and an interme- 
diate, largely porous structure. The reverse surface (fig. 6d) was similarly con- 
stituted, but the ribs were occasionally indistinct, and the foramina near the base 
were changed into short tubuli, which were inclined downwards, and occupied 
the whole area. Internally the characters were also similar to those on the 
opposite side, except that the thickness of the network was greater. A compari- 
son of the front and back of a branch will prove however two differences ; first, 
that the foramina adjacent to the foot of the coral are in one case filled up, in 
the other elongated downwards (fig. 6 c); and secondly, that the ribs on the front 
are not overlaid where the obliterations occur, while the equivalent reverse por- 
tion is wholly covered with short tubuli. Under every observed state, the fora- 
mina were bounded by the lamin composing the reticulated fabric ; and it is 
consequently inferred, that they had not an independent structure, previously to 
their altered character, but were simply canals in the substance of the coral. 
Tab. XVIII. A. figs. 7 to 7h. 
The fossil delineated in this Table agrees so closely with Herr Roemer’s! repre- 
sentation of Chrysaora pulchella, that a specific identity can scarcely be doubted. 
? Verst. Norddeutschen Kreidegebirges, p. 24. tab. 5. f.29. From the upper chalk-marl of Gehrden 
and Quedlinburg. 
