n8 TABULATE CORALS. 



treble row by the suppression of the others. Tabulae well 

 developed, complete. Mural pores generally few in number, 

 of large size, and irregular in their distribution. 



Obs. There is no genus in the entire series of the Favo- 

 sitida which presents greater difficulty than the present one, 

 as regards its satisfactory definition and separation from allied 

 types. So much so is this the case, that a strong disposition 

 has been shown by some of our most distinguished palaeontolo- 

 gists to reject the genus Alveolites altogether, and not without 

 reason, since it is certain that the forms which have at various 

 times been included under this name are of very different affin- 

 ities. The difficulties which environ this subject have been 

 elsewhere discussed at some length by Mr R. Etheridge, jun., 

 and myself (Journ. Linn. Soc., vol. xiii. p. 353, 1877); and I 

 shall avail myself largely of the memoir just referred to in what 

 follows. Since this paper was written, however, I have been 

 able to obtain much additional material throwing light upon the 

 genus, and am therefore able to speak more decidedly upon 

 some points which at that time appeared doubtful, as well as to 

 modify in some particulars the opinions therein expressed. 



The genus Alveolites was originally founded by Lamarck in 

 the first edition of the ' Systeme des Animaux sans Vertebres ' 

 (published in 1801), p. 375, for the reception of a single Devo- 

 nian species which he described under the names of A. subor- 

 bicularis and A. escharoides, and for which the former title has 

 been subsequently retained. The original definition is, " Poly- 

 pary stony, thick, globular, or hemispherical, formed of numer- 

 ous concentric layers, which are superimposed one upon the 

 other, each layer formed by the union of alveolar, subtubular, 

 prismatic, contiguous cellules [or tubes], forming a network on 

 the surface." In the Hist. Nat. des Anim. sans Verteb. (pub- 

 lished in 1816), vol. ii. p. 184, the same definition is given with 

 very slight alterations, the principal change being that the genus 

 is now made to include incrusting forms. In the second edition 

 of Lamarck's Hist. Nat. des Anim. sans Verteb. (published in 

 1836), the portion relating to the corals was revised by Milne- 



