DENDY—REPORT ON THE CALCAREOUS SPONGES 21 
The sponge is a single Sycon person, which was evidently attached in life by a 
contracted base, but there is no stalk. The body of the sponge has an inflated 
appearance, especially on one side, and is surmounted by a well-developed oscular collar, 
not a mere fringe of spicules but a thin membrane supported by a special skeleton. The 
surface is coarsely bristly from the projection of large oxea, which point obliquely 
upwards. The specimen figured measures about 10 mm. in total height, including the 
oscular collar, and 4°8 mm. in maximum transverse diameter; while the height of the 
collar is about 3mm. Specimen A was 9:25 mm. in total height, with a transverse 
diameter of 5 mm. in the middle of the body, but the height of the oscular collar was only 
1:75 mm. The colour in spirit is pale yellow. 
The wall of the sponge, about 1°25 mm. thick in the middle of the body, surrounds a 
wide gastral cavity. It gradually diminishes in thickness upwards to the base of the 
oscular collar. The canal system is like that of Grantia, with long, unbranched (some- 
times ? slightly branched) radial chambers, approximately circular in transverse section, 
united laterally with one another throughout their length, and with narrow, irregularly 
shaped inhalant canals in the interstices between them. 
There is a thick dermal cortex (ectosome), with abundant mesogloea, overlying the 
distal ends of the radial chambers. This cortex is excavated by large, irregular sub- 
dermal cavities, which extend inwards, around and between the ends of the chambers, 
and communicate with the inhalant canals. The small dermal pores are scattered over 
the surface of the sponge. 
There is also a thick gastral cortex, with abundant mesogloea which projects into the 
gastral cavity around the bases of the apical rays of the gastral quadriradiates. The 
gastral cortex is pierced by short exhalant canals, into which the radial chambers open 
either singly or in groups. The junction of each chamber with the exhalant canal is 
marked by a well-developed diaphragm. 
The arrangement of the skeleton in most respects agrees with that of a typical 
Grantia. The dermal skeleton is composed of stout, tangentially placed triradiates, 
arranged in several layers, and the huge oxea project obliquely through it from deep down 
in the chamber layer. The triradiates of the dermal cortex sometimes appear to be 
invading the chamber layer. The gastral cortex is made up chiefly of the facial rays of 
large gastral quadriradiates, whose strongly developed apical rays project into the gastral 
cavity, accompanied by minute microxea. It also contains small quadriradiates which, in 
several close-set tiers, surround the exhalant canal of each radial chamber, with their 
apical rays projecting into the canal. The skeleton of the chamber layer is articulate and 
many-jointed, the proximal joints being formed by characteristic subgastral sagittal quadri- 
radiates with minute, rudimentary apical rays and long, straight, centrifugally directed 
basal rays, often more or less grouped in bundles. The skeleton of the oscular collar is a 
close interlacement of oxea and radiates. The former run lengthwise and parallel with 
one another and with the basal rays of the radiates; the latter have very long, slender 
basal rays and stouter paired rays extended almost at right angles to the basal ray, and 
most of them have straight, sharp-pointed apical rays. 
