90 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 14, 



not being necessary in this instance, nor the latter in Siderastrcea 

 (jalaxea, which has interspaces uniformly on a level with the margin 

 of the abdominal hollows. A third example may be mentioned, as it 

 occurs in a coral the visceral receptacles of which have no central 

 structure during growth, and only rudimentary lamellae while in that 

 condition. The Heliopora ccurulea of M. de Blainville possesses 

 considerable, uniformly level intervals formed of minute, continuous 

 tubes crossed by laminae. The additional cavities occur almost wholly 

 towards the upper extremity of the foliations or lobes, but they are 

 decidedly formed in the intermediate composition. The first indica- 

 tion is a shallow, irregular depression, due probably to a natural dis- 

 ruption of the tissues which had previously fabricated the tubuli. 

 The little area is, apparently, soon modeled into a circular shape ; 

 and the slightly projecting perpendicular plates, which would have 

 formed the sides of minute tubes, had no breaking-up of mem- 

 branes occurred, become the first-formed narrow or rudimentary 

 lamellse. The network at the base of the hollow, arising from the 

 discontinued structure, continues open for a time, but is ultimately 

 covered by a solid layer, the first of the laminae, by which the area 

 is successively crossed. This is perhaps one of the simplest modes 

 by which the operation is effected among Anthozoa ; all that is 

 wanted being a mere receptacle for the stomach-sac. 



The statements given in a former paragraph respecting fissiparous 

 developments, as well as those just mentioned, prove that in each of 

 the two great processes, previously existing solid materials and animal 

 tissues are associated in the young cavity with others which are new, 

 and contribute towards its perfect formation. These combinations 

 also plainly show, that however the modes of effecting the results 

 may differ, they are but modifications of one plan. Distinctions 

 nevertheless exist deserving the most attentive consideration, when 

 an attempt is made to establish subordinate groups. In bipartitions, 

 the contents of only one mature cavity are concerned ; while in inter- 

 polations those of two or more contribute to the task : again, in fis- 

 siparous separations the additions are confined to the dividing struc- 

 ture, and are as necessary to the perfecting of the parent's composition 

 as to that of the offspring ; but in the other process old and new la- 

 mellae or plates are intermingled throughout the circuit of the young- 

 area, and entirely confined to it. These are obvious differences, which 

 require no skill in discovering ; and though the experienced physio- 

 logist can alone appreciate their importance, the study of them with 

 others of a similar nature cannot be too earnestly pursued by the 

 palaeontologist. 



The next coral to be considered was labelled ^' Cricopora gracilis,^'' 

 but without stating whether the specific term had been adopted or 

 was considered new*. The Isle of Wight fossil, however, is clearly 

 not identifiable Avith the Cric. gracilis of M. jMichelinf, nor with 



* Consult Dr. Fitton's iMemoir, Quart. Journ. Geol. Soc. pp. 302, 327*, vol. iii. 

 Aug. 1817. 



t Iconoj^raphic Zoophytologiquc, p. 4. pi. 1. fig. 8. 



\ 



