AND PHYSIOLOGY OF THE SPONGIAD^. 
1105 
Halyphysema, Bowerbank. 
Sponge consisting of a hollow basal mass from which emanates a single cloacal fistula. 
Skeleton ; spicula of the base disposed irregularly ; spicula of the fistula disposed 
principally in lines parallel to the long axis of the sponge, without fasciculation. 
In its form and habit the type of this genus closely resembles Polymastia brevis ; but 
the total absence of fasciculi in its construction at once marks it as a distinct genus, 
although a closely allied one. The type species. If. Tumanowiczii, is remarkable as 
being the smallest known British sponge ; it rarely exceeds a line in height. The base 
of the sponge resembles in form the half of an orange cut at right angles to its axis ; and 
the fistular cloaca is usually dilated at its distal extremity. I have been unable to 
detect either oscula or pores in any of the numerous specimens I have examined ; but, 
from the general accordance in structure with the genera Alcyoncellum and Polymastia., 
there is a strong presumption that the oscula will prove to be congregated at the distal 
extremity of the cloacal fistula, as in those genera. Plate LXXIII. fig. 3. 
CiocALYPTA, Bowerbank. 
Skeleton composed of numerous closed columns, each consisting of a central axis of 
compact, irregularly elongated reticulated structure, from the surface of which 
radiate, at about right angles, numerous short simple cylindrical pedicels, or stout 
fasciculi of closely packed spicula ; the distal ends of each pedicel separating and 
radiating in numerous curved lines, which spread over the inner surface of the der- 
mal membrane, separating and sustaining it at all parts, at a considerable distance 
firom the central axis of the skeleton. 
T^kis genus is allied by its structural peculiarities, to a certain extent, to Dictyocylin- 
drus\ Bowerbank, Hyalonema, Gray, and Alcyoncellum, Quoy et Gaimard. The central 
axial column of the skeleton is composed of elongated stout reticulations of siliceous 
spicula, closely resembling the corresponding tissues of the axial column of a Pictyocy- 
lindrus ; but the space between the surface of the column and the inner surface of the 
dermis is not filled, as in that genus, by the usual interstitial structures of the sponge, 
it is completely and widely separated from the dermis in a manner very similar to that 
of the structure of the greatly elongated cloacal appendage of Hyalonema mirabilis as 
it appears in its present condition in the most perfect specimens in the British Museum 
and in the collection of Dr. Gray. There is this difference between the structures of the 
two genera. The coriaceous dermis surrounding the beautiful spiral axial column of 
Hyalonema is very thick, and is abundantly furnished with projecting oscula; and it 
does not present any indications of lateral pedicels, either on its inner surface or on the 
surface of the axial column, while these organs are abundant in G. yenicillus, and its 
dermis also is comparatively thin and delicately reticulated. 
The dermal portion of the sponge in C. penicillus, and the reticulated tissues on its 
inner surface, closely resemble the corresponding tissues in Alcyoncellum in their struc- 
7 L 2 
