the Oreensand compared with those of existing Species. 119 



posed to tlic beating of the most tempestuous seas. Hence 

 we shall not be surprised to find re]M:escntatives of these in the 

 Ilaldon deposit. 



They will be found in Plates IX. and X. figs. 32-37 and 

 59-74 respectivelj. 



Some of the hexternate heads, as figs. 30, 31, and 33, might 

 either have belonged to Schmidt's Ancorinida3, in which are 

 included Stelletta &c. (Atlant. Spong. Faun.), or to the peri- 

 phery of the Dactylocalycidai (see Dr. Bowerbank's figures of 

 D. Masoyii and D. Bowerhankii^ 2, 3, and 6 respectively, Proc. 

 cit. 1869, pi. vi.); for they all have such hexternate heads for 

 their periphery, although those of the Dactylocalycid^ appear 

 to be the thickest and to have the stoutest shafts, which, in 

 the fossil species are, for the most part, unfortunately broken 

 ofi". 



Where, however, the heads have not been so expanded, 

 although still irregularly hexternate (as in PI. X.), the shafts 

 have consequently become more developed, and therefore have 

 partly remained, thus giving us facsimiles of the spicules 

 which characterize the Pachytragia? generally, — that is to say, 

 Schmidt's Ancorinidje and Geodidinai (Atlant. Spong. Faun.). 



The figures 37-39 and 72-74 inclusively all appertain to a 

 quadrifid or quaternate system, which, whether belonging to 

 the Coralliospongiffi or to the Pachytragite, only find their pa- 

 rallel now, so far as I am aware, in Hyalonema {Carter ia, 

 Gray), where the minute feathered spicules have tlie like heads 

 in miniature — some of the large ones with more extended 

 arms also — and all the long large ones a crucial branching of 

 the axial canal, with more or less inflation in the centre. 



In Aslconema setiihalense, Kent, a similar condition exists ; 

 but here the minute spicules are liexradiate, and the large long 

 ones present a liexradiate cross, with more or less central in- 

 flation. It is almost impossible to see all six arms of the cross 

 at the same time in the long spicules ; but the quadrilohate 

 form of the inflation in many, if not most, is satisfactory 

 evidence of this condition when the cross is not otherwise 

 visible. 



Returning to the Pachytragi^, we find that the ternate spi- 

 cules of the circumference, in the absence of silicified fibre for 

 support, are accompanied by strong acerate, fusiform, smooth, 

 and, generally, slightly curved spicules, which not only abound 

 in the interior, crossing each other in all directions to form the 

 skeleton, but frequently project somewhat beyond the surface 

 in connexion with the peripheral spicules — also that this form 

 is often accompanied by strong acuate spicules of the same 

 kind, in which one half of the spicule seems to be more or 



