18 R. KIRKPATRICK. 



The radial bundles of styles proceed from base to periphery, and usually do not 

 penetrate the surface ; the exotyles form pyramidal tufts which originate just below 

 the cortex, this arrangement being well seen in young specimens. 



Specimens were obtained from Winter Quarters, Flagon Point, 10-20 fms. ; from 

 No. 12 hole, 25-30 fms. ; and from McMurdo Bay up to 20 fms. 



SPHAEROTYLUS CAPITATUS. 

 (Plate XII., fig. Ic, Plate XIII., figs. 8-13, and Plate XIV., figs. 1-4.) 



1882. Radiella schoenus Sollas (20. p. 163), Nomen nudum. 

 1885. Polymastia capitata Vosmaer (32. p. 16). 

 1808. Sphaeroti/liis capitatus Topsent (26. p. 244). 



The single specimen (XII. Ic) is attached to a block of volcanic rock on which 

 specimens of S. antarcticus and Polymastia invaginata are growing. The sponge is in 

 the form of a flattened dome 1'5 cm. in diameter and 5 mm. in height, with a small 

 papilla 5 mm. in length, rising from near the centre of the upper surface. From one 

 side of the specimen slender bud-bearing stalks arise to a height of 2-4 mm. ; 

 sometimes the buds are in linear series (XIV. 2), sometimes zigzag (XIV. 4). 



The axes of the stalks are the prolongations of radial fibres, and consist of tyles. 

 The buds, which vary from '5 mm. to 1*25 mm. in diameter, bristle with the sharp 

 points of small and medium-sized tyles. 



The largest bud (XIV. 3) has exotyles, and shows all the stages of their develop- 

 ment. Firstly, there is a thickening of the distal end of an ordinary sharp-pointed 

 tylostyle, which becomes cylindrical ; then the end becomes roughened, and finally 

 clavate. 



Merejkowsky (14. p. 4, PL I., figs. 8, 12, and PL III., figs. 1-3) figures buds 

 forming on stalks at the summits of the papillae of Polymastia mammillaris (Rinalda 

 arctica) from the White Sea. The stalks and buds strikingly resemble those of 

 Sphaerotylus capitatus, excepting that the latter grow direct from the general surface 

 of the body and not from the summits of the papillae. 



Merejkowsky gives an interesting account of the development of these buds, which 

 drop off from their stalks, and become flattened and disk-like as they rest on the 

 bottom. The surface becomes covered with debris which the spines help to retain. He 

 supposed that the decaying organic debris served as nutriment, which was directly 

 absorbed by the surface of the young sponge. 



The flagellated chambers are diplodal. 'The colour of the specimen in 

 spirit is pale yellow. The body presents a surface uniform to the naked eye, but 

 under a strong lens the summits of the club-shaped exotyles are visible. These 

 spicules arise in bundles of the shape of inverted cones, the apices of which are a short 

 distance below the cortex. 



The cortical skeleton is formed of slender tyles. There is no sub-cortical layer of 

 tangential spicules. 



