GENERA OF FA VOSITID.E. 83 



less to attempt to discuss and illustrate more than one or two 

 types. Some forms, as has been seen, have the thin walls 

 of Favosites proper, and are clearly generically inseparable from 

 the more typical massive examples of this group. The forms 

 now under consideration, however, have the thickened walls 

 and general structural characters of Pachypoj'a, Lindstrom, 

 under which head they ought clearly to be placed. The 

 species which I have here selected is one highly characteristic 

 of the Devonian, and I have made a careful macroscopic and 

 microscopic study of a large number of specimens which I have 

 personally collected from rocks of this age in Devonshire, in 

 the Eifel, and in Canada. Nevertheless I do not feel certain 

 as to the limits of the species, nor am I sure that all the forms 

 given in the foregoing list of synonyms are really only varia- 

 tions of a common specific type, though I am disposed at 

 present to take this view. 



The figures which I have given (PL IV., figs. 3 - 3 <^) are all 

 taken from a single form, which I found to be very abundant 

 at Gerolstein, in the Eifel, and which I consider as certainly 

 identical with those figured from the same region by Goldfuss 

 under the name of Calamopora polyinoi'pha, var. ramoso-digitata 

 — these being identified by the high authority of MM. Milne- 

 Edwards and Haime with the Alveolites cervicornis of De 

 Blainville. Nor can I doubt the substantial identity of this 

 form with the Favosites i^etiadata of De Blainville, — the only 

 tangible difference between them being the unimportant feature 

 that the branches of the latter inosculate with one another. 

 On the other hand, Milne-Edwards and Haime, in the * Poly- 

 piers Fossiles,' state that the larger calices of F. cervicoiiiis have 

 a diameter of nearly two millimeters, and that the walls are 

 only " un peu epaisses ; " whereas they give one millimeter as 

 the diameter of the calices in F. retiailata, and speak more 

 decisively as to the thickness of the walls of its corallites. 

 Goldfuss's figures, however, which are usually very reliable, 

 show hardly any appreciable difference in the size of the coral- 

 lites in these two forms, both having the majority of the calices 



