284 TABULATE CORALS. 



Silurian specimens they very seldom project above the surface, 

 and do not form the strancje monticules which are so common 

 on the surface of the Russian Lower Silurian specimens. I 

 suppose that these clusters are continuations from the original 

 and larger zooecia, which were budded out round the smooth 

 centra when the colony was in its Ceramopora stage. In some 

 there is seen a sort of ' reversion,' the zocecia on the surface of 

 the Montiailipora having again assumed the unmistakable 

 characters of Bryozoon, becoming oblique and radiating as 

 in a Ceramopora. Longitudinal sections, however, demon- 

 strate that there is a direct continuation from the tubes of the 

 Alonticiilipora into those of the Ceramopora, or that the former 

 arain have chang-ed into the latter." 



Having thus described what he believes to be the mode of 

 development in Monticulipora petropolitana, Pand., Dr Lind- 

 strom proceeds to give an account of the development of a 

 Silurian fossil which he terms Monticulipora ostiolata, and which 

 he identifies with the Trematopora ostiolata of Hall (Pal. N.Y., 

 vol. ii. p. 152, PI. XL., fig. 5), with xh^ N ebulipora papillata of 

 M'Coy {M. papillata, E. and H., Brit. Foss. Cor., p. 266, PI. 

 LXn., fig. 4), and with Thccostegites heinispherictis of Ferd. 

 Roemer (Sil. Faun, of Tennessee, p. 25, PI. IF, figs. 3, 3 a). 

 This form is stated by Dr Lindstrom to commence its existence 

 as a Discoporella, and then to pass into what may be called the 

 " Fistulipora stage," each cell being now "surrounded by a 

 mass of small vertical, circular, or polygonal tubes having the 

 appearance of a coenenchyma," and all the tubes, both large 

 and small, being " traversed by tabulee of the same incomplete 

 type as those which characterise Monticulipora." ^ From this 

 ''Fistulipora stage" the colony is stated to pass next into what 

 Dr Lindstrom calls the " Thccostegites stage," in which the 

 interstitial tubes become covered with "a thin smooth calcare- 

 ous membrane," leaving the larger tubes open, and causing 



1 I do not understand precisely what Dr Lindstrom may mean by " incomplete" 

 tabula;; but the tabuls of almost all the Monticulipora; that I have examined, 

 except M.frondosa, D'Orb., are just as " complete " as they are in the typical mem- 

 bers of the Favositida:, 



