334 Mr. R. Hope on two new 
of Bowerbank’s genus Microciona, taken in a strict sense, 
that is to say, of that section of the genus which agrees with 
the type, M. atrosanguinea, in the possession of monactinal 
megasclera of three kinds, with “navicular” isochele and 
toxites as microsclera. It is in this stricter sense alone that 
the generic term Microciona is used throughout this paper. 
In all other respects the classification followed is that of 
Messrs. Ridley and Dendy, to whose diagnoses of the genera 
&c. in their Report on the ‘ Challenger’ Monaxonida I refer. 
I propose for this sponge the specific name of strepsitoxa 
(Gr. otpépa, I twist), from a peculiarity of the toxa referred 
to below. 
Microciona strepsitoxa, n. sp. 
The sponge coats about four square inches of the flat valve 
of a scallop-shell (Pecten, sp.), attaining in the furrows of the 
shell a maximum thickness of about 1 millim. Its colour, 
when fresh, was scarlet, but in spirit it rapidly and completely 
faded to a dead white. Surface, when fresh, smooth ; in the 
dry state hispid, from the projecting ends of the spicular 
brushes of the skeleton. ‘The oscula are numerous and run 
deep into the sponge; the pores small and generally distri- 
buted over the surface. 
The skeletal columns, as usual in the genus, rise vertically 
from the base to the surface; they are slender at the base 
and rarely branched, and they end in thick brushes of 
spicules which, spreading out obliquely in contact with each 
other, are traversed horizontally by sheaves of long slender 
styles imbedded in the sponge-substance. As usual also in 
Microciona, the main skeletal spicules increase in length 
towards the surface of the sponge, the shortest, as a rule, 
forming the base of the columns. ~ 
Spiculation.—Megasclera, three :— 
1. Styles, sometimes straight, but generally slightly curved, 
constricted about one diameter above the base, sometimes 
smooth, but usually basally spined or tuberculated. They 
vary greatly in length, ranging from *480 to °636 millim., 
with a few much shorter; breadth °0105 to ‘012 millim. 
(figs. A, 1 and 2). 
2. Straight orslightly curved, tapering, entirely spined styles 
and tylostyles, varying in length from about °1 to :2 millim. ; 
average breadth about ‘006 millim. (fig. A, 3). 
3. Long, smooth, slender, subclavate styles, from about *25 
to °31 millim. long by about -004 millim. broad. With a 
high power the heads frequently appear slightly roughened 
(fig. A, 4). 
