GENERA OF FAVOSITID^E. 41 



plete transverse partitions, which are placed at variable 

 distances, and rarely anastomose. Most usually, the tabulae 

 are approximately horizontal ; but they may be markedly con- 

 vex or concave. Certain species (F. favosa, Goldf.) have been 

 distinguished by the curvature of the tabulae ; but this appears 

 to be a very variable character, differing even in different parts 

 of the same specimen, and it cannot be employed in the diag- 

 nosis of species. Similarly, it is not uncommon to find that 

 the tabulae are so bent as to give rise to a series of marginal 

 pits or depressions, which in some specimens are extremely 

 regular, and impart an apparently characteristic appearance to 

 the tubes. This feature, however, is also not constant, even 

 in the same individual, and cannot be looked upon as of 

 specific value. 



While the typical species of Favosites possess " complete " 

 tabulae, there are others in which these structures have the 

 form of imperfect plates, which extend into the visceral cham- 

 ber transverse to its axis, but do not divide it into a succession 

 of completely separate vertical storeys. These " incomplete " 

 tabulae were regarded by Milne-Edwards and Haime as being 

 of generic value, and these authors placed all those forms 

 possessing them in the genus Emmonsia (loc. jam cit.) The 

 fact, however, that it is by no means uncommon to meet with 

 single specimens in which some of the tubes have the irregular 

 and incomplete tabulae of Emmonsia, while others have the 

 regular and complete tabulae of the type-forms of Favosites 

 the same tube sometimes exhibiting both these conditions in 

 different parts of its course is quite sufficient 'to show that the 

 separation of Emmonsia as a distinct genus cannot be carried 

 out in practice. 



Lastly, there are various species of Favosites in which, in 

 addition to, or in the absence of, complete tabulae, the inner 

 surfaces of the tubes are rendered rough by the presence of 

 numerous horizontal projecting lamellae, which extend only a 

 short distance into the visceral chamber, and which often have 

 a more or less leaf -like or tongue -like character. These 



