26S TABULATE CORALS. 



posed strata, which generally have a thickness of from half an 

 inch to three-quarters of an inch. 



In addition to specimens from the Carboniferous Limestone 

 of Moscow, I have examined a number of examples which I 

 have collected from the Carboniferous Limestone of the north 

 of England — a formation from which C. radians is quoted by 

 Milne-Edwards and Haime. The British specimens entirely 

 resemble the Russian ones in their shape and general configu- 

 ration, in their long basaltiform corallites, and in the composi- 

 tion of the corallum out of concentrically disposed strata formed 

 by a periodic development of tabulse at corresponding levels. 

 At the same time there are some differences between the two 

 sets of specimens. The English examples (PI. XIL, figs. 4 c 

 and 4 d) have rather smaller tubes, which are more regularly 

 polygonal, and more uniform in shape, and which are slightly 

 more thin-walled than is the case in Russian specimens. The 

 tabulee also are not nearly so numerous, and few of these struc- 

 tures are develoj^ed between the concentric zones of these 

 diaphragms, by which the whole colony is divided into super- 

 imposed strata. At the same time, there is the same total 

 amalgamation of the walls of the corallites, and in certain of 

 the tubes we always see the same tooth-like projection indicat- 

 ing the approaching division of the corallite into two. Upon 

 the whole, therefore, in spite of the differences just noted, I am 

 not disposed to regard the British specimens as more than a 

 mere variety of the typical C. radians of Russia. 



As has been already pointed out, C. radians, Fischer, is 

 closely allied to C. (Alveolites) septosus, Flem., C. {Alveolites) 

 depressus, Flem., and C. hyperboretis, Nich. and Eth., jun., with 

 which it forms a most natural group ; and all of these forms 

 are characteristic of the Carboniferous Limestone. The last 

 mentioned of these species is easily separated from C. radians 

 by the lamellar and expanded form of the corallum, as well as 

 by other characters, and C. depressus, Flem., is similarly separ- 

 able by the very small size of its tubes. On the other hand, 

 C. {Alveolites) septosus, Flem., so nearly approaches C. radians 



