RELATIONS TO EXTINCT ORGANISMS. 



87 



cerned, there are some peculiarities in the general fades of 

 the former which would at once lead the observer to separate 



Fig. 14. — Minute structure of Ccrantopora. A, Tangential section of Ccramopora O/iiociisis, 

 Nich., from the Cincinnati Group of Oliio, enlarged eighteen times; B, Part of a longi- 

 tudinal section of the same, similarly enlarged, showing the presence of tabulae ; C, Part 

 of a transverse section of the same, similarly enlarged, showing the thickened cell-walls ; 

 n. Part of a tangential section of an undescribed species of Ceramopora, from the Wen- 

 lock Limestone of Dudley, enlarged eighteen times; E, Vertical section of the same, 

 similarly enlarged, showing the well-developed tabula. 



them as distinct. Thus, the tubes of which the colony are 

 composed always open upon the surface in an oblique manner, 

 reminding one of Alveolites rather than of Monticiilipora, and 

 the calices are invariably either very irregular in shape, or 

 are, more usually, distinctly crescentic or lunate, one lip of the 

 aperture being strongly curved. As regards internal structure, 

 the general conformation of the skeleton is quite like that of 

 some of the IleterotrypcE amongst the Monticuliporoids, the 

 tubes being comparatively thin-walled in the vicinity of their 

 points of origin, but becoming thickened by a secondary 

 deposit of laminated calcareous matter as they approach the 

 surface. There are, also, small tubules intercalated amonof 

 the proper tubes of the colony ; and lastly, there exists a 



