58 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 4,
which, I conceive, were not in communication with the internal
tube-spaces.
In fig. 7 modifications of this structure may be observed; for there appear to have been no tubes on the lines of the axes; and this gives the nodal area a simpler character.
It will be perceived that the above description reproduces very nearly Mr. T. Smith's "octahedral" structure.
Perhaps what I have said, together with the figures illustrating this paper, may help towards a comprehension of the affinities of the Ventriculites. Their structure is better preserved in some respects in these nodules than elsewhere. The external surfaces are better shown. And in connexion with this part of the subject I may mention what appears a singular fact. I have a specimen of so-called Porospongia ocellata which bears the impression of the Ostrea carinata at the angle formed by the auricular expansion near its hinge. The ocelli are entirely confined to the surface of contact, and upon the other surface there are none apparent.
Spicula are scattered throughout the mass of these specimens, especially in P. ocellata. They have the character of spongespicula, but appear not to be siliceous; they are for the most part straight, and tapering towards one end.
I now pass to the consideration of the ordinary nodules, which are obtained by the ton weight, whilst those just described are quite rare fossils.
Upon a close examination of their surface (fig. 8) it will be perceived that they have a peculiar granulated surface like that of leather, and that they are constantly wrinkled in places, as if by the contraction of an integument. These wrinkles are more numerous and marked wherever the surface is somewhat pitted or depressed, while protuberant parts are often smooth. It is not easy to speak with certainty; but the surface seems to be minutely porous.
The wrinkles do not follow any determinate direction, although in the digit-like forms they are usually more or less transverse to the length. The constancy of these characters of the surface, and their general shape according with the idea of growth, renders it certain, in my opinion, that these nodules were organic bodies. But it is not easy to determine their affinities.
My original idea was that they were sponges. However, upon submitting some thin sections of them to Dr. Bowerbank for his opinion, he informed me that he could not perceive that they exhibited any traces of sponge-structure. This led me to compare them with the Alcyonium digitatum. When this polypidom dies, it parts with some of the water which distends it, and the integument becomes wrinkled and roughened with irregular papillae, which cover the cells of the polyps. It is not easy to obtain a specimen of the recent zoophyte unaltered in shape, because, when it parts with the water contained in it, it takes the form of any surface with which it is in contact. But, out of many specimens kindly sent to me by Mr. Damon, I have so far succeeded in making some plaster casts of the recent zoophyte, that, after being coloured, their close resemblance to the
