16 R. KIRKPATRICK. 



is 8 mm. high, 8 mm. in length at the base, and 4 mm. in thickness. In some the 

 pile has been rubbed off, exposing the smooth, fleshy cortex. Some of the specimens 

 are growing on large stones ; others are free, but with numerous embedded pebbles in 

 the fleshy basal pad. 



In many specimens the oscule is invisible, being entirely retracted within a cavity 

 below the summit, and with the opening of that cavity, contracted to a point and 

 concealed by the surface pile of spicules ; a vertical section reveals the oscular papilla 

 in its cavity. One specimen has two oscular papillae. The general structure of the 

 skeleton recalls Trichostemma, which likewise has a basal pad, with fibres radiating from 

 base to periphery, and with a cortex of tyles. T. sarsii also has the stellate groups of 

 tyles between the fibres of the choanosome. The basal pad is composed of stellate- 

 celled colleuchyma, the collencytes with their branched anastomosing processes being 

 embedded in a clear, gelatinous matrix. 



Most of the specimens were dredged in the neighbourhood of Winter Quarters in 

 depths of 10-30 fms. ; one came from near Mounts Erebus and Terror, 500 fms. 



SPHAEROTYLUS, Topsent (26. p. 244). 



Polymastidae, massive ; provided with tylostyles, and with exotyles in the form 

 of spherotyles or spherostyles. 



This genus was established by Topsent to contain Polymastia capitata, Vosmaer 

 (32. p. 16). I have slightly extended the original definition by the addition of the 

 word " spherostyles," because one of the two species of Spltaerotylus in the present 

 collection has exotyles in the form of spherostyles, i.e., exotyles with the proximal 

 inner end simply rounded and not enlarged into a knob, a spherostyle being a style 

 with the distal or outer end enlarged. The difference between a spherostyle and a 

 spherotyle is hardly of generic importance, consequently Sphaerotylus must include 

 forms with spherostyles. 



Hitherto only three Astromonaxonellid sponges with exotyles have been described, 

 viz., Tylexocladus joubinii Topsent, Proteleia sollasii Ridley and Dendy, and 

 Sphaerotylus capitatm (Vosmaer). The 'Discovery' collection contains two species 

 of Sphaerotylus, a new one S. antarcticus, and one which appears to me to differ in no 

 important respect from the Arctic species S. capitatus (Vosmaer). 



SPHAEROTYLUS ANTARCTICUS. 



(Plate XII., figs. 1A-16 and Plate XIII., figs. 1-7.) 

 Sphaerotylus antarcticus Kirkpatrick (10a. p. 272). 



Sponge, dome-shaped or spheroidal, attached or free. Surface beset with a 

 covering of long spherostyles, and with a dense short pile of cortical microtyles. 

 With several usually elongated papillae with or without a large terminal orifice. 

 Dermal pores distributed over the cortex, each pore opening into a single tubular 



