88 BRITISH STROMA.TOPOROIDS. 



interior of the vesicles so arranged as to leave a larger or smaller number of clear 

 lines which radiate from the convex outer margins of the vesicles towards their 

 shorter inner sides (Plate VIII, fig. 5). This is one of the points concerning 

 which one is unfortunately left in the dark owing to the imperfect preservation of 

 the specimens ; for out of a large series of sections, taken tangentially, transversely, 

 and longitudinally, I fail to find one in which this structure is so clearly shown as 

 to allow of a definite interpretation of its nature, though all show it more or less. 

 All that I can say is that it reminds one, to some extent, of the arrangement of 

 the rudimentary radial pillars on the surface of the vesicles of Bosenella macrocystis 

 (Plate VII, fig. 12). x 



The most characteristic structures of the Stromatoporoids, however, are the 

 " radial pillars," and I am now able to show that apparently similar structures 

 exist in Beatricea in a well-marked form. Here, again, we have the disappointing 

 fact that these structures, owing to the state of preservation of the specimens, are 

 not uniformly to be recognised. Even in specimens in which they are well shown 

 they are only to be found in portions of the coenosteum, having apparently dis- 

 appeared elsewhere ; or if they are present, the ordinary vesicular tissue is apt to 

 be wanting. In certain specimens, however, the vesicles and the radial pillars are 

 preserved in the same section (Plate VIII, fig. 4), in which case the pillars are seen 

 as strong, apparently hollow rods, which are directed outwards in a radiating 

 manner from the axial canal towards the circumference, and which are united to 

 one another by the vesicular tissue. In this case, therefore, the structure is essen- 

 tially the same as is observed in the genus Labechia, E. and H. 



In another, very large specimen, for which I am indebted to Mr. Whiteaves, 

 the inner layers of vesicular tissue, in the vicinity of the axial canal, show no traces 

 of the radial pillars ; but these latter structures are very well preserved in the 

 peripheral zone of the coenosteum. Transverse or longitudinal sections of this 

 region of the skeleton show a general structure quite similar to what we might 

 expect in any Stromatoporoid. Such sections (Plate VIII, fig. 6) show a series of 

 strong radial pillars radiating from the central portion of the skeleton towards the 

 circumference, and united by well-marked concentric " laminae," which undulate 

 in conformity with the surface-elevations. Both the pillars and the laminae are 

 composed of granular matter, showing well-marked dark points. The ordinary 

 vesicles are present here and there among the pillars, and run parallel to the 

 laminae ; but they are mostly wanting, in which case the concentric laminae seem 

 to be formed out of the granular lining which is seen in all the vesicles. Tangen- 

 tial sections, taken close to the circumference (Plate VIII, fig. 7), also show 



1 In one section of Beatricea nodulosa, Bill., I have noticed perpendicular calcareous septa 

 crossing the vesicles, but whether or not this has anything to do with the appearances described above 

 I am unable to say. 



