Lower Helderberg Fauna. 265 



expanded and dentate terminus of one arm is supported upon 

 the central dentate portion of the arm belonging to the spicular 

 element laterally adjacent, whose center does not lie in the same 

 canal face as that of the first, but half a mesh-length above or 

 below it. (R\uff1. c.) He explains DuNCA^q's figures (Ann. Mag. 

 Nat. Hist., 1879, vol. lY, pi. IX, figs, la, 2, 2) by supposing that 

 they have been drawn from a tangential section of the sponge in 

 which the real union of the spicules can not be distinguished. 



Neither Hinde nor Kauff makes any mention of the re- 

 curvature of the tripodal ray to the node of the second row 

 beneath or toward the center, as described by Ulrioh. Kauff 

 does say, however, that possibly the aborted fourth ray may, in 

 some cases, be prolonged outward to join the node of the next 

 spicule above, on the same corner of the canal, thus strengthening 

 the connection and materializing the angle. He thinks, in fact, 

 that he has observed this prolongation in one instance. On the 

 other hand, the atrophy of the fourth ray seems natural, if it is 

 considered that the inflated terminations of the arms are often 

 so strongly prolonged that they impinge upon the central node 

 of the spicule with which they are bound. This lateral 

 outgrowth in the course of time must stunt the fourth arm 

 (Kacff 1. c). ' 



My own observations on Hindi a confirm those of Ra^uff in 

 every essential particular. The only exception is that the spicules 

 in the Lower Helderberg specimens seem a little more slender, 

 and the whole spicular net-work more light and elegant in con- 

 sequence. Neither have I seen the prolongation of the fourth 

 ray above alluded to. 



Upward of 175 specimens of Hindia -fibrosa have been 

 examined by me, and I have observed the individual spicules 

 well preserved in but one instance. In this example, the charac- 

 ter of the spicules themselves and of the whole spicular frame- 

 work, has been maintained with a fidelity and perfection that 

 leaves little to be desired. The specimen in question has an outer 

 coating of pyrite. The interior is limonite, becoming somewhat 

 ochreous toward the center. The sponge skeleton appears as a 

 polished and exceedingly perfect cast in which the shape and 

 mode of union of the constituent spicular elements are clearly 

 portrayed. 



34 



