On the Genus Cladochonus. 291 



In our remarks which follow we first give some notes on the 

 relation of Cladochonus to Aulopora, and we next describe the 

 microscopic structure of one or two species, more particularly of 

 Cladochonus crassus. 



2. Relations of Cladochonus to Aulopora. — The general resem- 

 blance subsisting between Cladochonus and Aidopora is so close as to 

 strike the most superficial observer, and this is particularly the case 

 between the aberrant C. crassus, M/Coy, and the larger forms of the 

 latter, the habit of the coral being in both cases the same. It would 

 lead us too far, upon the present occasion, to enter at any length into 

 the general structure and relations of Aidopora, nor are our investiga- 

 tions on this head as yet completed ; but there are one or two points 

 in this connexion to which we may with advantage draw attention. 

 Aidopora has generally been believed to possess corallites with 

 entirely open visceral chambers, no tabidce being present ; and in 

 this has been placed the principal distinction between this genus and 

 young colonies of Syringopora. We have, however, made microscopic 

 sections of two forms of Aidopora, one, a large species from the 

 Devonian deposits of Canada (Fig. 1, d — ■/), and the other the well- 

 known A. repens of the Eifel Limestone (Fig. 1, g, h) ; and in both 

 we find that the cavities of the tubes are crossed by strongly arched 

 transverse partitions or tabular. The invagination of the tabula? is 

 not so conspicuous as in Syringopora, but cross-sections of the tubes 

 present a very similar appearance to that seen in the latter genus ; 

 and it seems clear that the internal structure of Aulopora is essen- 

 tially the same as that of young colonies of Syringopora. We are 

 not, however, prepared to assert that tabulae are present in all the 

 species of Aulopora, nor can we enter here into the question of the 

 relations between this genus and Syringopora. 



Coming next to the relations between Cladochonus and Aulopora, 

 we have figured (Fig. 1 c) a longitudinal section of what we believe 

 to be a corallite of Cladochonus Michelini, Edw. and H., from the 

 Carboniferous rocks of Scotland. It must be borne in mind, how- 

 ever, that though one may identify a given specimen as belonging 

 to such a small Cladochonus as C. Michelini, it is really impossible to 

 be certain that one has not in fact to deal with a detached corallite of 

 Aidopora ; and there must therefore always attach a certain doubt to 

 such sections as Fig. 1 c. That this section is really one of Cladochonus 

 Michelini, E. and H., we believe, because the specimen from which 

 it was taken had all the external features of this species, and it also 

 occurred with others also having the characters of this form (Fig. 1, 

 a and b), and again because we know of no Aulopora in the Carboni- 

 ferous rocks of Scotland, from the breaking up of which fragments 

 of this nature could have been derived. Further than this, however, 

 we cannot go. All, therefore, that can be said is, that we find, in this 

 and in similar longitudinal sections, that the visceral chamber of the 

 corallite is sometimes, though apparently not invariably, crossed by 

 delicate curved tabulae (Fig. 1 c). Sometimes we have failed to 

 detect these partitions, and in any case they are always remote, and 

 very delicate in structure ; so that they may be chiefly recognizable 



