124 TABULATE CORALS. 



In the most typical species of Alveolites, tlie corallites are 

 excessively oblique to the principal plane of the corallum, 

 those which open on the circumference of the mass most so, and 

 those in its centre least. A. stiborbictdaris, Lam., offers the 

 extreme type of this condition, while A. Indianensis, Rom., 

 though an unquestionable Alveolites, presents the minimum 

 amount of obliquity of its tubes. It has been pointed out by 

 Lindstrom that A. Foiigtii, E. and H., primitively possesses 

 erect corallites, which only become reclined in the course of 

 growth ; and upon this ground this high authority has placed 

 the species in Favosites. Upon the whole, however, though 

 formerly disposed to adopt the same view, I think it safer to 

 go by the adult characters of the corallum, which would seem 

 to place this curious transitional form in Alveolites. 



Owing, also, to the obliquity of the corallites, the calices in 

 Alveolites open obliquely upon the surface, one lip being shorter 

 than the other, and the aperture being more or less transversely 

 elongated, its shape being in general subtriangular, semilunar, 

 or subrhomboidal. 



The walls of the corallites in Alveolites are invariably thin, 

 as conclusively shown by thin sections ; there is no marked 

 thickening due to the deposition of concentric lamellae of scler- 

 enchyma in their interior, nor are the tubes notably, or as a 

 rule at all, expanded towards their mouths. All forms re- 

 sembling Alveolites in appearance, but with abnormally thick- 

 ened walls, must find a place either in Pachypora, Lindst., or 

 in Ccenites, Eichw. 



The vmral pores are usually few in number, and of compara- 

 tively large size ; but it is certain that this character cannot be 

 used as one of generic value, precisely the same feature occur- 

 ring in Pachypora. 



The septal system varies much in its development in Alveo- 

 lites. As has been seen, Milne-Edwards and Haime regarded 

 the presence in the interior of each corallite of three elongated 

 teeth or septal ridges, which may be reduced to one, and which 

 represent the septa, as the leading character of the o-enus. I 



