FA VOSITID&. 



33 



tures appear to be wholly obsolete (e.g., in Stenopora, Lonsd.) 

 The most typical condition of matters is, that the septa should 

 be present in the form of vertically disposed rows of longer or 

 shorter spinules. The number of these vertical rows varies, 

 but is most commonly between ten or twenty. In Ccenites, 

 Eichw., the septa are reduced to one or more tooth-like ridges, 

 which appear to be confined to the thickened portions of the 

 tubes, close to their mouths; and in Alveolites, Lam., a similar 

 reduction of the septa may take place, though the walls are not 

 thickened, and the septa may be wholly wanting. In Arceopora, 

 Nich. and Eth. jun., the septa subdivide and anastomose with 

 one another to a greater or less extent; and in Nyctopora, 

 Nich., they assume the form of marginal ridges or lamellae, 

 their typical spiniform character being lost. 



Lastly, the visceral chamber in all the Favositida is inter- 

 sected by a greater or less number of transverse partitions or 

 " tabulae." Typically, these tabulae are " complete " that is to 

 say, they pass completely across the visceral chamber as so 

 many unbroken horizontal plates ; but this is not invariably 

 the case. Sometimes, however (as in Favosites hemispherica, 

 Yand. and Shumard), the tabulae are " incomplete," having the 

 form of tongue-shaped laminae, which project to a greater or 

 less extent into the visceral chamber, often anastomosing or 

 dividing at their free edges, but not passing quite across the 

 tube. Very commonly " complete " and " incomplete " tabulae 

 are found coexisting ; and this is particularly the case with the 

 comparatively rudimentary and imperfect tabulae which occur 

 in many species of Favosites, and which Dr Rominger terms 

 "squamulae," assigning to them, as I think erroneously, a 

 septal origin. Finally, there are genera, such as Michelinia, 

 De Kon., in which the tabulae are convex, and unite so freely 

 among one another as to give rise to a kind of subvesicular 

 tissue, not unlike the cellular tissue which fills the visceral 

 chamber of the Cystiphyllidce, though usually much less per- 

 fectly vesicular, and interrupted every now and then by a 

 complete tabula. 



c 



