PROTOZOA. 
583 
SiLICEA. 
Order 1, Vitrea. 
The order Vitrea is established by Wyville Thomson (1. c.), and 
is characterized as follows ; — 
Vitrea. Sarcode in small quantity, very soft; never containing formed 
horny matter, either fibrous, membranous, or granular. The skeleton con- 
sists entirely of siliceous spicules, either separate (in fascicles or scattered) or 
anastomosing and combined into a continuous siliceous network. The sar- 
code contains small spicules of a different character from the general spicules 
of the skeleton, and of complicated forms. The spicules, whether of the 
skeleton or of the sarcode, may all be referred to the hexradiate stellate type. 
Ex. Hyalonema, Dactylocalyx. 
A list of the known genera and species of Vitreous Sponges is 
given (p. 119) ; and remarks are appended ^^on the conditions of 
the sarcode in this group, on the siliceous skeleton/^ on the 
general structure of the Sponges of the group, and on the re- 
lations of the group, the author^s impression being that it is 
through this order that the Sponges pass into the Radiolaria. 
Hahrodictyon, g. n., Wyvilld Thomson, 1. c, p. 12G. Sponge-body subcy- 
lindrical, tubular, attached by a slightly contracted base. The walls of the 
tube composed of a perfectly 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 spi- 
cules of the skeleton all essentially of the hexradiate form, free and separate 
from one another, or rarely connected in groups of two or three. The spi- 
cules of the sarcode very numerous, “ floricomo -hexradiate stellate ” and 
various simple and branched modifications of the hexradiate type. This 
genus is established for the Alcyoncellum corhicula of Valenciennes, and for 
the A. speciosum of Quoy & Gaimard. 
JIahrodictyon corhicida, Val. Alcyoncellum corhicida,Ysl.f — Hetero-‘ 
tella corhicula^ Gray, is described by Wyville Thomson, 1. c. p. 129, pi. 4. 
figs. 1 a~lf. — II. sjjeciostwi, Quoy & Gaimard (sp.),=^. speciosum, Q. & G., 
= Corbitolla spcciosa, Gray, is described by Wyville Thomson, 1. c. p. 131, 
pi. 4. figs. 2 & 2 
Euplectella. Semper’s ^Einige Worte vdoer Eiiplectella aspergilhim, Owen, 
und seine Bewohner ’ will be found translated in Ann. & Mag. Nat. Hist. 
July 1868, pp. 26-30 {vide Zool. Record, 1867, pp. 665, 676). 
Claus, in his memoir on Euplectella aspergillum, describes at great length 
the structure of the spicules of this species. The memoir is accompanied by 
an excellent photograph of two specimens of this beautiful Sponge. 
Euplectella oweni, sp. n., Ilerklots Sc Marshall, 1. c. p. 438, Japan. 
Ilyalothouma * is the name given by Ilerklots & Marshall 1. c. p. 437, to 
* We have been unable to find out the exact date of publication of this 
genus, which equals Gray’s genus Semper ella. 
