COLLECTED BY THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 433 



area, but the whole sponge is covered by a cribriporal membrane, with pores measur- 

 ing about 0*03 mm. in diameter. The main skeleton is formed in the usual way of 

 radiating bundles of megascleres, but the dichotrisenes, anatrisenes, and protrisenes 

 for the most part pierce the sterrastral layer, although a few lie beneath it. The 

 dermal membrane is supported on the cladomes of the dichotrisenes, and is separated 

 from the layer of sterrasters by a space about 0'2-0'3 mm. in width. In places 

 the anatrisenes and protrisenes project some distance beyond the surface of the 

 sponge. The cortical oxea and minute cortical anatrisenes project slightly, and 

 cause the finer hispidation of the surface. 



The sterrastral layer varies in thickness in the different specimens from about 

 0*55 mm. to 1 mm. Large subdermal cavities occur between the dermal membrane, 

 which is crowded with minute strongylospherasters, and the sterrastral layer. 



Numerous pigment cells, brownish in colour, are found between the dermal 

 membrane and the sterrastral layer. 



Spicules. — (l) Dichotrisenes. — Shaft tapering gradually to the rounded proximal 

 end, and measuring 2'5-3 mm. in length by 0'07-0'l mm. beneath the cladome. 

 Protocladi 0*1 mm. by 0'05-0'06 mm. Deuterocladi 0'175-0"25 mm. in length. 

 Cladome about 0*6 mm. (2) Anatrisenes. — Shaft up to 3'5 mm. in length by 0*012- 

 0*015 mm. under the cladome, rounded at the proximal end. Cladi '03-0 "06 

 mm. Chord about 0'07 mm. (3) Cortical anatrisenes. — Length '3-0*4 mm. by 

 0*0025-0*004 mm. Sometimes rounded at the proximal end. Cladi up to 0*008 

 mm. in length. (4) Protrisenes. — Shaft 2*5-3 mm. in length by 0*012-0*019 mm., 

 rounded at the proximal end. Cladi 0*025-0*06 mm. (5) Somal oxea. — Length 

 2-3 mm. by 0*045-0*06 mm., tapering at each end to a rather blunt point. Some- 

 times one, or, more rarely, both ends rounded off. (6) Cortical oxea. — Length 0*25- 

 0*3 mm. by 0*005-0*008 mm., tapering at each end to a blunt point, which is some- 

 times rounded off. (7) Sterrasters. — Spheroidal in shape, but somewhat flattened. 

 Diameter 0*1-0*12 mm. (8) Somal strongylospherasters. — Diameter 0*005-0*008 

 mm. ; very short, cylindrical actines. Extremely abundant in the dermis, but common 

 also in the interior of the sponge. (9) Choanosomal spherasters with small centrum, 

 passing into oxyasters. Actines 0*005-0*01 mm. in length, the whole aster having 

 a diameter of 0*013-0*024 mm. 



This species differs from the majority of Geodia species in having the dichotrisenes 

 piercing the sterrastral layer and supporting the dermal membrane on their cladi 

 at a certain distance above it. Among the species in which a similar arrangement 

 of the dichotrisenes occurs are G. perarmata Carter (2 and 5) and G. peruncinata 

 Dendy (5). The Scotia species differs, in particular, from the former in the absence 

 of a definite, basin-shaped, oscular area, and in the presence of minute cortical 

 anatrisenes, and from the latter in the possession of cortical oxea and of brown 

 pigment cells in the outer layer of the cortex. There are, as well, certain differences 

 in the character and measurements of the spicules. G. sflixroides (Kieschnick) 



