Mr. H. J. Carter on the HexactineilidEe. 365 



At first I thoiig-lit, from the presence of these long fusiform 

 spicules in great abundance and of large size in D. subglobosa, 

 that the latter must be identical with I), i^umicea ; but the 

 general globular cup-like form of D. subglobosa, together with 

 the muricated summits of the tubercles on the joints and the 

 pappiform rosette with straight capitate rays, all cause it so 

 far to differ from D. pumiceus and D. pumicea. 



Myliusia callocyathes differs from the foregoing in the thorny- 

 appearance of its fibre — that is, in the minute blunt spines 

 which are scattered over the fibre of the foregoing species 

 being much enlarged, elongated, and pointed, — also in the rays 

 of the rosettes in most instances being sigmoid instead of 

 straight, and ari'anged en fleur-de-lis^ and in the absence of 

 the linear fusiform spicules. Dr. Bowerbank's figure of its 

 structure would be perfect were it not combined with a surface- 

 spicule of MacAndreioia azorica, as before stated (fig. 6, l. c), 

 Avhich of course is an oversight, the latter belonging to quite 

 a different system of sponges, viz. the Lithistidge. 



Myliusia Grayij both in general form and structure, has 

 many distinguishing characters, especially that which consists 

 in an octahedral lantern-like appearance of the joints, produced 

 by the vitreous fibre stopping short of the joint and proceeding 

 thence directly on from one arm of the sexradiate spicule 

 to the other, so as to leave the centre intact and visible through 

 the interstices. This is best seen in the younger portions of 

 the fibre, as the older ones, by thickening, render the cross in 

 the centre obscure. Schmidt's figure from a fossil species 

 (Taf, ii. fig. 16, op. cit.) would illustrate this well, were it not 

 for the absence of the sexradiate cross in the centre, which may 

 have become absorbed in the deciduous specimen previously 

 to fossilization, after the manner to be hereafter explained. 



The spicules of Euplectella aspergillum are enveloped in 

 ladder-like silicified fibre, such as is seen in some of the homy- 

 fibred sponges ; and the characteristic rosette for the most part 

 has its rays arranged en fleur-de-lis, while the rays themselves 

 present the peculiarity of being clavate with claw-shaped spines 

 on the outer side of tlie head. The latter is repeated in Habro- 

 dictyon sjjeciosum and H. corbicula, where the sarcode is not 

 vitrified. It is also present in Euplectella cucumer, which 

 appears to be a mixed species in point of structure ; that is, 

 while the general structure in the figure looks as if unaccom- 

 panied by vitreous fibre, the lid not only appears to be con- 

 solidated by it, but in the index to the plate is stated to be 

 " soldered," the only time that this word is used in the whole 

 paper. Thus, a fragment of a Euplectella of this nature, pre- 

 sented to the British ]\rus;'uin by " Admiral Sir W. Belclier," 

 Ann. & May. N. Hist. Scr.4. Vol. xii. 25 



