126 Prof. W. Thomson on the ‘ Vitreous” Sponges. 
something in the wonderful complexity of design and profusion 
of ornament in the siliceous skeleton which reminds one 
strongly of the PoLycysTINA; and even, in some cases, the 
special forms of the spicules are repeated in the two groups. 
(Compare pl. 12. fig. 1, pl. 17. fig. 4, pl. 18. fig. 15, pl. 21. fig. 7, 
pl. 32. figs. 10, 11, pl. 33. figs. 6, 7, &e. of Haeckel’s ‘ Die 
Radiolarien’). As yet, we know nothing of any of the spe- 
cies in a living state.’ ‘The sarcode is certainly somewhat dif- 
ferent in character from that of the other groups of Sponges, 
—softer and more mobile, less loaded with granular formed 
matter, and more transparent. For sarcode in this condition 
we should be inclined to anticipate a somewhat higher form of 
vital activity. It remains to be seen whether there may be 
any approach by the extension of any form of pseudopodial 
rocesses to the condition of the sarcode in the RHIZOPODA. 
nder a strong impression that it is through this order that 
the Sponges pass into the RADIOLARIA, I have placed the Port- 
FERA VITREA at the head of the series of siliceous Sponges, be- 
ginning with those genera in which the siliceous elements are 
most independent and varied, and the sarcode least consistent. 
I believe that Dr. Gray has rightly indicated the base of the 
order by placing the Flower-baskets next the Esperiade, 
which I should certainly regard as the inosculating family of 
the HALICHONDRIDA. 
(Porifera Silicea). Order I. VITREA. 
HABRODICTYON, n. g. 
1. Alcyoncellum, De Blainville, Quoy & Gaimard, ‘ Voyage de l’Astrolabe,’ 
Zoologie, vol. iv. p. 302. Paris, 1833. 
2. Alcyoncellum, Deshayes and Milne-Edwards, in Lamarck’s ‘ Animaux 
sans Vertébres,’ vol. 11. p. 589 (1836). 
3. ee cds ie (misprint for Alcyoncellum), Trans, Zool. Soe. vol. iii. 
52 : 
4, badges owerbank, Phil. Trans. and British Spongiade, vol. i. 
p. 174 (1865). 
5. Euplectella, Gray, Ann. & Mag. Nat. Hist. vol. xviii. p. 487 (1866). 
6. Corbitella, Gray, Proc. Zool. Soc. for 1867, p. 530. 
7. Heterotella, Gray, Proc. Zool. Soc. for 1867, p. 551. 
Sponge-body subcylindrical, tubular, attached by a slightly 
contracted base. ‘T'he walls of the tube composed of a per- 
fectly irregular network of bundles of siliceous needles 
loosely and irregularly arranged in sheaves crossing one 
another at low angles, and connected by a small quantity of 
soft mucilaginous sarcode. The spicules of the Bat ir all 
essentially of the hexradiate form, free and separate from 
one another, or rarely connected in groups of two or three. 
The spicules of the sarcode very numerous, “ floricomo- 
