196" LIVERPOOL BIOLOGICAL SOCIETY. 
Order I. MYXOSPONGIE. 
Halisarca rubra, n. sp. (Pl. X., figs. 1 and 2.) 
New species of Halsarca have been described so fre- 
quently, which have afterwards been shown not to belong 
to that genus or even not to exist at all, that it is with 
some reluctance that I establish the new species Halzsarca 
rubra. The specimen was dredged on the “ Spindrift” 
Expedition in July, 1889, off Holyhead, from a depth of 
about fifty fathoms. It encrusted both valves of a living 
Mytilus edulis with thin brick-red patches, the entire thick- 
ness of the sponge being 0°45 mm. Its surface showed a 
somewhat wavy outline, which condition was apparently 
solely caused by the hairs of the Mytilus projecting through 
it, and the sponge growing for a short distance upwards 
along those hairs. Oscula and pores were not visible to 
the unaided eye. 
Vertical sections showed that the outer portion of the 
sponge had suffered, so that its structure could not be made 
out satistactorily. ‘The figure (see PIX] feai)ioren 
therefore is somewhat diagrammatic. The inner and 
ereater portion of the sponge was well preserved (PI. X., 
fig.2). There isa ‘‘ dermal membrane” between the outer 
world and subdermal cavities, about 0'014 mm. in thickness. 
The subdermal cavities are flat, and seem to be distinct 
from the wide irregular cavities of the canal system. 
Oscula and pores could not be detected. 'The flagellated 
chambers are round or oval, with a diameter of 0°08 to 
0:14 mm. The size of the collar-cells, of which however 
the collars and flagella were never seen distinctly, is about 
0:006 mm. ‘The mesoderm consists of fibrous tissue. Im- 
bedded in it are large red pigment-cells, 0°02 to 0°026 mm. 
in size, more or less oval and pretty numerous. Their 
nuclei are small, and sometimes only indistinctly seen. 
