292 Prof. Nicholson and R. Ethericlge, jun. — 



by the fact that the surrounding matrix has penetrated into the 

 visceral chamber to a certain depth, and that its lower limit is 

 marked by a clean and regular curved line. So far, then, as the 

 evidence at present before us goes, it would appear that the 

 internal structure of Cladochonus Michelini is essentially the same as 

 that of those species of Aulopora which we have submitted to micro- 

 scopic examination. ]t seems to be "tabulate," and it does not, 

 therefore, conform to the definition of the Zoantharia tubulosa given 

 by Milne-Edwards and Haime. 



On the other hand, Cladochonus crassus, M'Coy, exhibits an 

 entirely different structure, unlike that of both C. Michelini, E. and 

 H., and the species of Aulopora which we have here figured. "We 

 shall deal with the internal structure of this remarkable species at 

 greater length hereafter (see Fig. 2) ; and we need only say now that 

 the visceral chambers of its corallites appear to be entirely open and 

 free from transverse partitions of any kind, while the wall is greatly 

 thickened, and exhibits in parts a very exceptional and abnormal 

 differentiation of its tissues, which entitles it to take rank as a distinct 

 generic type. 



Cladochonus Michelini, Edwards and Haime. 



Fyrgia Michelini, Hi. and TJ., Polyp. Foss. Terr. Pal. 1851, p. 310, t. 17, f . 8, a & b. 



„ „ Quenstedt, Handb. d. Petrel 1852. p. 638, t. 56, f. 18. 



„ „ Milne Edwards, Hist. Nat. des Corall. 1860, vol. iii. p. 322. 



„ ,, Fromental, Introd. a 1' etude des Polyp. Foss. 1861, p. 318. 



Cladochonus Michelini, de Koninck, Nouv. Rech. sur les Anim. Foss. etc. 1872, p. 

 153, t. 15, f. 6, and 6 a. 



Observations. — It is unnecessary for us to redescribe this species 

 after the full and detailed notice of Prof, de Koninck, our object now 

 being to make a few remarks on the microscopic structure of the 

 corallum. 



As before noted, there must remain some doubt as to the reference 

 of any given specimen to this species, rather than to the detached 

 corallite of an Aulopora. The specimens, however, which we have 

 selected for sectioning appear to us, for the reasons before given, to 

 be really referable to C. Michelini, E. and H., and they appear to 

 correspond in their general structure with Aulopora repens. That 

 is to say, they generally exhibit a tubular visceral chamber (Fig. 

 1, c) crossed by a few irregular curved tabulge, but otherwise un- 

 interrupted. In other specimens we can detect no traces, however, 

 of transverse partitions. The walls of the corallites are solid 

 throughout, and we have failed to find any evidence of the peculiar 

 reticulate structure of the wall which characterises C. crassus, 

 M'Coy. 



Loc. and Horizon. — Catcraig Quarry, near Dunbar, in shale above 

 the Skaleraw Limestone ; Skaleraw Quarry, near Dunbar, similar 

 horizon — Lower Carboniferous Limestone Series — Coll. Geological 

 Survey of Scotland. 



Collector. — Mr. James Bennie. 



