REPORT ON THE MONAXONIDA. 193 



0'09 by 0"0045 mm.; the spines are sharp, prominent, and very abundant, except in the 

 centre of the shaft, where they are rather scarce. 



This remarkable sponge is one which may be easily recognised both by its external 

 appearance and by its spiculation, the latter being quite unmistakable. 



The skeleton is arranged on decidedly an AxineUid type, especially as regards the 

 manner in which the large, radiating, stylote spicules are surrounded by dense sheaves of 

 small, slender styli. The general appearance of the sponge is thus decidedly Axinellid, 

 1)ut no sponge belonging to this group has hitherto been found with the spined oxeote 

 microsclera, which closely agree in form with the microsclera of Sj^ongiUa lacustris. 



Locality. — Simon's Bay, Cape of Good Hope; depth, 10 to 20 fathoms. Two 

 specimens. 



Genus Thrinacophora, Eidley (Pis. XXIII., XXIV., XXXVL, XL.). 



1885. TJirinacophora, Eidley, Narr. ChaU. Exp., vol. i. pt. ii. p. 572. 



1886. Thrinacophora, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 483. 



Sponge ramose, with a dense central axis of spiculo-fibre ; megasclera styli and (or) 

 oxea, and (in some species) cladostrongyla. Microsclera, present in the form of tricho- 

 dragmata. 



This genus was first founded by Ridley {loc. cit.), for the reception of the very 

 remarkable species which we have called Thrinacophora fiiniformis. It was at first 

 thought that the curious furcation of one of the megasclera in this species would prove 

 to be a character of generic importance, but our subsequent examination of the collection 

 ilisclosed another sponge (TJirinacophora cervicornis), which agrees so closely with 

 Thrinacophora funiformis that the two seem to us to be, at any rate for the present, 

 generically inseparable, although the former possesses none of the branching spicules. 

 Hence we have decided that in this case, as in the Desmacidonidse, the microsclera are the 

 most reliable guides to classification, and we consider the presence of the trichodragmata, 

 taken in conjunction with the Axinellid arrangement of the skeleton, as the most 

 important generic character. This one character separates the genus at once and 

 aljsolutely from all other known genera of AxineUidse. 



Possibly the branched spicule of Thrinacophora funiformis is comparable to the 

 " bidentate " stylus of the only known species of Dendropsis, and it is noteworthy in 

 this connection that both these genera stand apart from the remaining AxineUidse in the 

 possession of microsclera, though the microsclera are of very different form in the two 

 cases. We have already ^ had occasion to point out the special bearing of the presence 

 of a branched spicule in T]irinacop>hora funiformis upon the question of the relationship 

 of the Monaxonida to the Tetractinellida. 



' Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 157. 

 (ZOOL. CHALL. EXP. — PART. LIX. — 1887.) Nnn 25 



