366 MESSRS. H, A. KICHOLSON AND E. ETHEEIDGE 



are perhaps warranted in attacMng great weight to this negative 

 evidence, seeing that we have examined a large series of speci- 

 mens from different localities, and from different beds, in different 

 states of preservation, and by means of polished sections and thin 

 transparent slices as well as by broken surfaces. "We are disposed, 

 then, to believe that mural pores are really wanting in A. septosa, 

 Mem., A. depressa, Flem., and Chcetetes radians, Fischer ; and we 

 may add that Milne-Edwards and Haime expressly affirm the 

 absence of pores in the latter. If this view be correct, it is clear 

 that the two first-mentioned of these forms can no longer be re- 

 tained in Alveolites, from which they further differ in their com- 

 paratively erect corallites and their non-oblique calicos. 



As regards the second point, namely the nature of the so-called 

 " septal tooth," this process is very conspicuous in A. septosa and 

 in Chcetetes radians, and can be most readily examined by means 

 of thin sections cut at right angles to the course of the tubes. In 

 A. depressa the same processes exist, though not so conspicuous ; 

 and we entertain no doubt as to their being of precisely the same 

 nature in all these forms. By Milne-Edwards and Haime this 

 tooth in A. septosa and A. depressa was regarded as representing 

 a single primary septum ; and they compared it with the elongated 

 septal ridge of A. suhorbicularis — an analogy which is increased 

 by the fact that the process has sometimes one or two smaller 

 teeth opposed to it, as in A, dentieulata, E. & H. Against this 

 view, however, it must be urged that the tooth-like process of A. 

 septosa and A. depressa is by no means universal in its occurrence, 

 nor constant in its development. It is only present occasionally, 

 in certain of the calicos, and is often absent over considerable 

 areas, whilst it varies in size from a hardly perceptible protuber- 

 ance up to a vertical lamina extending halfway or more across the 

 visceral chamber. These facts militate strongly against the com- 

 parison of these processes to the septal ridges of A. suhorbicu- 

 laris ; whilst several of our specimens of A. septosa show in addi- 

 tion numerous obscure longitudinal striae, which we believe to be 

 the true representatives of the septa. On the other hand, Lons- 

 dale regarded the tooth-like processes of Chcetetes radians, Fischer, 

 as being of the nature of inflections of the walls of the corallite 

 preliminary to its fission into two tubes. This view is supported 

 by the easily observed fact that the mode of increase in C. radians, 

 as well as in A. septosa and A. depressa, is clearly by fissiparity ; 

 and it is further supported by the very variable length of the 



