new Genus oj Devonian Corals. 



519 



cientlj large series of thin sections, since we then find all 

 possible gradations to exist between the specimens of the first 

 group {^^ piliformis " group) and those of the second (" stel- 

 limicans'^ group). Indeed, a single slide will sometimes 

 exhibit almost all the transitional stages which conduct us 

 from the one group to the other. Thus we find certain 

 specimens in which the corallites, either throughout the entire 

 corallura or merely here and there, have their visceral cham- 

 bers quite free from the darker material. Even in such 

 specimens (PI. XV. figs. 5, 6, and also woodcut, fig. A) we find, 

 however, that the walls are not uncommonly slightly thick- 



Fig. 



V W f 



V w 



A, A few cells from a slide of H. stromatoporoides, Roem., taken 

 from a part "wliere the visceral chambers of the corallites are tilled 

 only with clear crystalline calcite, and the walls are only slightly 

 altered. Fig. B. A few cells from another part of the same slide, in 

 wliich the radiating crystalline strnctnre is incompletely developed, 

 tlie walls of the corallites being still discerjiible and the visceral 

 chambers partly unaffected (tilled v^'itli matrix). Fig. C. A few 

 cells from another part of the same slide, in whicli the walls are still 

 to be seen, but the crystallization has assumed its characteristic 

 stellate form. Fig. D. Anotlier part of the same slide, in which 

 the walls of the tubes have become completely obliterated, and we 

 see only the dark stars, the centres of these corresponding with the 

 centres of the visceral chambers. Fig. E. A few cells from a slide 

 of another specimen, in which the walls are left, and the rays of the 

 crystalline stars are seen cutting through the walls, and thus uniting 

 with contiguous stars. Fig. F. Part of a vertical section of the 

 same, completely crystallized ; and fig. (^\. Another vertical section 

 incompletely infiltrated : v, dark lines representing the axes of the 

 visceral chambers : lo, faint vertical lines, representing tlie walls of 

 the corallites ; /;, portions of the visceral chambei'S infiltrated only 

 with clear calcite, and still showing tabulae ; c, calices. All the 

 figures are enlarged twenty -four times. 



