74 THE VOYAGE OF H.M.S. CHALLENGEE. 



dermal reticulation is seen to be arranged in a rotulate manner, similar to the dermal 

 reticulation of Bowerbank's Desmacidon rotalis ^ ( = Esperella rotalis), but Hardly so 

 regular as shown in his figure, (h) Main; it is difficult to make out any definite 

 arrangement. In the cylindrical pieces there appears to be a central, rather loose core 

 of thick spiculo-fibre ; one can also distinguish thick bands of spiculo-fibre running 

 more or less vertically to the surface ; on approaching the surface the fibre opens out 

 slightly and the points of the spicules composing it project a little way beyond the 

 dermal membrane, thus causing the minute hispidation already noticed. The spiculo- 

 fibre of the main skeleton is generally dense and thick. 



Spicules. — (a) Megasclera; of one kind only, viz., tylostyli (PL XV. figs. 7, 7a), 

 tapering towards the base so as to form a neck and then enlarging slightly to form 

 the small head ; towards the apex the spicule tapers very gradually to a sharp point ; 

 size about 0'4 by 0"0145 mm. {h) Microsclera; (1) large and peculiarly-shaped, palmate 

 anisochelse (PI. XV. figs. 16, 16a, 166, 16c), measuring about 0'072 mm. in length, 

 with the large end 0"036 mm. wide; for further particulars as to their shape see the 

 figures [loc. cit.). These spicules are frequently seen to echinate the skeleton fibre, being 

 themselves arranged in groups, with their truncated small ends placed close together 

 upon the spiculo-fibre and their large ends radiating outwards (perhaps the truncation 

 of the small ends may be due to this peculiar habit). Plenty of the large anisochelse 

 are also found lying freely in the tissues. Numerous smaller anisochelse also occur, 

 which difi"er from those just described in having the large end relatively of greater 

 size ; they difler also slightly in general shape, but they have the cup-shaped, 

 truncated small end found in the larger ones, and we are inclined to think that they 

 are young forms of the latter {vide PI. XV. fig. 16c). There are also some minute 

 anisochelse, probably still younger forms of the same. Neither of the small forms 

 appear to be attached to the skeleton fibre, as the large ones are. (2) Very large, 

 thick, smooth, contort sigmata (PL XV. fig. 13), something like the diancistra found (e.g.) 

 in Vomerula esperioides, nobis, but without the membranous expansions and with no notch 

 in the centre of the shaft; size 0*24 by 0"019 mm. These spicules are also very often 

 found adhering, usually by their backs, to the skeleton fibre, which thereby acquires a 

 very formidable appearance. (A similar arrangement of the large diancistra may be seen 

 in Vomerida esperioides, nobis, and in Hamacantha johnsoni, Bk., sp.) (3) Very 

 fine, single, scattered, smooth toxa (PL XV. figs. 12, 12a), measuring about 0"145 by 

 0-003 mm. 



This is a highly interesting species ; unfortunately, it is represented in the collec- 

 tion by only a few fragments. With, so far as we can judge, a very insignificant 

 external form, it combines a spiculation which in beauty and variety is hardly sur- 

 passed among the known Monaxonida. One of the most remarkable features about it 



' Mon. Brit. Spong., vol. iii. p. 327, pi. sc. figs. 8-14. 



