258 Mr. H. J. Carter on the 



voured to account by the fact that the calcareous fibre in 

 Millepora alcicornis, as the horny fibre in Hydractinia echi- 

 nata, appears first in small increments, which afterwards 

 become continuous in both instances; but in vain do we 

 look for the granular appearance in the fresh fibre of Mille- 

 pora alcicornis after it is fully formed ; so that it is just 

 possible that lapidification may have had a hand in this ap- 

 pearance. 



Stellate Venation. — The stellate venation consists of points 

 in the ccenenchyma more or less uniformly distant from each 

 other, from which flexuous rays, now represented by trans- 

 parent calcite, radiate in all directions, becoming branched 

 and subdivided as they go, until finally they terminate in 

 anastomosing with those of the neighbouring stellations and 

 in the cccnosarcal cavities of the ccenenchyma respectively 

 (PL XV. fig. 1). They appear to come into existence with 

 each lamina, as testified by the larger masses of rectilinear 

 ccenenchyma produced by the prevailing species of Stromato- 

 pora in Pit-Park Quarry at Dartington, wherein the lamina 

 may not be more than l-96th inch in thickness; hence the 

 least abrasion in making a section of such specimens may 

 take them away or bring them into view. The flexuous ray and 

 its branches may vary from 2 lines or less to 2 inches, chiefly 

 according to the species, with a diameter at its origin gene- 

 rally proportionate to its length, that of the latter being 

 l-24th inch *. The rays appear to be generally centred in 

 an elevation, and to descend, branching as they go, over the 

 sides of it to the plane surface of the species, following the 

 layer, whose undulation may be in proportion to the mamil- 

 lary projections on the free or natural surface, being greatest 

 in species like S. polymorpha, Goldf., while in others there 

 may be hardly any elevation perceptible, yet still the stellate 

 venations exist. Generally, too, they are centred in a special 

 enlargement like a cell, which may in some species have 

 more or less vertical extension ; but, whatever the centre may 

 be, it does not appear to have had an external opening, as 

 shown by Rosen's magnified illustration of a stellate vena- 

 tion from Stromatopora astroites (see tracing fig. 6, from tab. ii. 

 fig. 7), which had not even a central enlargement. How far 

 the extension of the flexuous ray may be confined to the 



* This is the largest that I have seen, and occurs in a species appa- 

 rently peculiar to Pit-Park Quarry, Dartington, of which Mr. Champer- 

 nowne has a specimen wherein the flexuous ray even exceeds these 

 dimensions. The largest seen by Baron Rosen is that of Stromato- 

 pora astroiteSf of which I have given a tracing (fig. 1) of the natural 

 size. 



