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 sponge- 

 spicula, 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 protu- 

 berant parts are often smooth. It is not easy to speak with cer- 

 tainty; 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 ex- 

 hibited any traces of sponge-structure. This led me to compare 

 them with the Alcyonium digitatmn. 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 specimenskindly 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 



