TETRAXONIDA 



299 



the dermis is supported by a tangential layer of tornota. Anisochelae and bipocilla are 

 present. 



In all respects, these specimens appear to be conspecific, despite obvious differences 

 in the shape and size of the acanthostyli and tornota and in the shape of the bipocilla ; 

 and this is even more clearly shown when they are compared with the specimens re- 

 corded under the various names included above as synonyms of /. chelifer. Nevertheless, 

 it must be confessed that the species is an unusually variable one. The variation in ex- 

 ternal form is not particularly marked, but in the spicules it is, although the series of 

 transitions which it is possible to construct leave no doubt as to the identity of all the 



t 



t' 



w 



Fig. 22. lophon proximum (Ridley): showing variation in ends of tornota. a, I. chelifer ostia-magna, Wilson 

 (type); b, I. chelifer, Ridley and Dendy (co-type: B.M. 87. 5. 2. 157); c, /. chelifer, Ridley and Dendy (type); 

 d, I. chelifer, Ridley and Dendy (Lambe's specimen); e, G iog\f, I. indentatus, Wilson (type); », /. lamella 

 indivisus, Wilson (type); /;, /. lamella, Wilson (type); i, I. pattersoni (Bowerbank), Ridley and Dendy 

 (Challenger Sts. 308 and 3ii);y, /. chelifer, Ridley and Dendy (Thiele's specimen); k, D 255; l-l" , D256; 

 m, D 251 ; n, D 739 ; 0, D 740 ; p, D 257 ; q, D 254, D 258 ; r, D431 ; s, D 252 ;<,/',£) 837 ; u, D 430 ; v, Alebion 

 proximum, Ridley (type); ro, lophon proximus (Ridley), var. reticularis, Hentschel. All figures x 1200. 

 Figs. a,f,g,h after Wilson ; fig. d after Lambe ; fig. j after Thiele. Fig. w from a preparation from the type. 



specimens with a single species. Some of the variations can be correlated, but only 

 vaguely, with increase in size, but nowhere is there so clearly marked a sequence as I have 

 described (1930) in /. radio tus, Topsent. For example, with increase in size the specimen 

 tends to become flabellate, either erect or spreading over the substratum ; generally, the 

 average size of the main acanthostyli and the tornota tends to increase, but the tendency 

 is not well marked ; the dermal skeleton is regular in young encrusting individuals and 

 becomes more diffuse and irregular in the larger forms, but is never lost ; and the bi- 

 pocilla tend to become trifoliate (or bifoliate) as the specimen increases in size. 



Other interesting features of the skeleton are: (i) the frequency with which the 



