SPONGES.-HALLMANN. 



195 



more closely resembles the first-mentioned, but is devoid of 

 surface grooves ; it is attached to a large water-worn stone by 

 an extensive basal disc. I'he 

 lamina in all three is from 6 to 

 8 mm. in thickness. The sponge 

 is very loose-textured ; near the 

 surface, adjoining main fibres are 

 often 0.5 to 0.8 mm. apart. The 

 fibres are comparatively slender — 

 probably never exceeding 100 ;< in 

 diameter. In the present speci- 

 mens the dermal membrane is 

 intact, and shows that the dermal 

 skeleton is precisely similar in its 

 formation to that of R. pauci- 

 spinus. The polygonal meshes of 

 the reticulation are very uniform 

 in size and average 120 j( in width. 



The following resume of its 

 spicular characters (omitting for 

 the moment the actual dimensions 

 of the spicules) shows this variety 

 to be unquestionably distinct from 

 any of the others. The smooth 

 megascleres are slenderer than in 

 all other cases, and are basally 

 neither expanded nor contracted ; 

 the principal and auxiliary styli 

 approximate in stoutness and in 

 shape and no longer permit of 

 their ready differentiation ; oxeote 

 modifications of the auxiliary and 

 dermal styli are of common occur- 

 rence ; and acanthostyles are com- 

 paratively rare and of small size. 

 On account of the great difficulty 

 in distinguishing between the prin- 

 cipal and auxiliary styli, I am un- 

 able to give the maximum length 

 of the former ; the diflRculty is fur- 

 ther increased by a certain amount 

 ol variability in respect to the 

 stoutness of spicules in different 

 specimens. The dimensions are 

 as follows : — 



Fig. 39 — A', t. var. anclio- 

 raius. a Principal styli. b 

 Auxiliary styli. b' Oxeote 

 modification of ditto. c 

 Special dermal styli. c' 

 Oxeote modification of ditto, 

 d Acanthostyli. e Larger 

 chela. f Smaller contort 

 chela. 



