500 " THETIS " SCIENTIFIC RESULTS. 



short distance, branch oflf at riglit angles and form the walls of 

 the pores at the surface; the connecting fibres are few and far 

 between, and are usually about 5 to I mm. in diameter. 



The mesh between the main fibres is usually elongate, and 

 about 0"3 mm. in diameter ; laterally and near the surface it 

 becomes round or rectangular ; all the fibres, especially the apices, 

 are very densely covered with echinating styli, the bases of 

 which are in close contact, and scarcely admit of additional 

 spicules. 



Meg^scleres : — (1) Short, stout, entirely and strongly spined 

 styli ; these echinate the fibres in vast numbers ; size 0'3 to 0'8 

 by 0-012 ram. 



(2) Stout, curved, smooth, acutely pointed styli; these occur 

 in the fibres and form radiating tufts at the surface ; size 0'3 to 

 0-5 by 00015 to 0-022 mm. 



(3) Curved or straight slender styli, with a tendency to become 

 subtylostyli ; chiefly dermal, but also scattered between the 

 fibres ; size 015 to 02 by 0-002 to 0-OOt mm. 



Microscleres : — (1) Long slender toxa mostly in bundles; scat- 

 tered ones have usually a long bend in the centre; size 2 to 

 0-3 by 002 mm. 



(2) Isochelse of the usual Clathria type; size O'OOS to 0-01 mm. 



CLATHRIA ARCUOPHORA, sp. nov. 



(Plate xlv., fig. 29.) 



Station 8. 



Sponge with a discoidal base, short peduncle, and an irregular 

 flabellate lamina ; the latter is 225 mm. in height and 170 mm. in 

 breadth, and from 3 to 5 mm. in thickness ; the pedicel is 70 

 mm. long and 15 mm. in diameter. Surface faintly marked with 

 longitudinal I'idges ; the lamina when viewed by transmitted 

 light appears as if it consisted of a series of coalescent branches, 

 between which many thin places and some perforations occur. 

 The dermal layer is thinly coated with a delicate membrane, 

 which is moderately charged with radiating tufts of smooth stylote 

 spicules ; these occur between the stout projecting styli at the 

 ends of the fibres. The oscula are regularly distributed over the 

 whole of the sponge ; they are from 0-5 to 1 mm. in diameter, 

 and about 1 or 2 mm. apart ; the intermediate spaces are finely 

 reticulate and minutely porous. 



Texture inelastic, brittle, and extremely harsh to the touch, 

 the latter character being due to the numerous projecting spicules ; 

 colour greyish-yellow. 



