256 J. G. WALLER ON AN UNDESCRIBED BRITISH SPONGE. 



obscure, all tend to show the alliance. But all these subsidiary 

 spicules show a feeble or imperfect development. 



One or two species given in the Challenger reports show a close 

 analogy in the associated forms alluded to ; in some cases they are 

 almost identical. I refer to Esjyeriopsis symmetrica in which similar 

 bihamates appear, and to Esperellafusca in which the anchorate 

 spicules are as near as possible the same ; I might also refer to 

 others therein figured, though the resemblances are less obvious 

 in these cases. 



The form of spicule belonging to the skeleton, distinguishing 

 this from any other of the genus referred to, is the large acerate, 

 subfusiform, which is associated with the acuate, typical of RapMo- 

 desma, and its close ally Desmacidon ; and it is this fact w4iich 

 makes the specimen interesting and which I considered thus to 

 demand a description. I propose to name it Raphiodesma ajinis. 



Description. 

 Sponge subrotund, in dry state fawn-colovir. Dermal 

 membrane, stout, spiculous. Hair-like acerate spicules disposed 

 somewhat in fasciculi, others singly dispersed, small. Larger 

 acerate spicules, few in number, also acuate spicules irregularly 

 dispersed. Anchorate spicules, tridentate, bidentate, inequipal- 

 mate. Skeleton, composed of large acerate spicules irregularly 

 disposed, with a somewhat open rete. With these also acuate 

 spicules as in membranes. Sometimes, on the latter, the anchorate 

 spicules show a tendency to the forming of rosettes, but not 

 complete. Besides this, it also exhibits in its structure very 

 delicate tricurvate spicules, and some curved forms, bihamate 

 irregularly developed. 



Explanation of Plate 14. 

 Raphiodesma affinis n. sp. 

 Fig. 1. Arrangement of spicules on dermal membrane, x 200. 

 „ 2. Part of skeleton in section. x 150. 

 „ 3. „ „ „ X 200. 



„ 4. „ „ „ X 150. 



,, 5. Anchorate spicules, front and side views. x 1200. 

 „ 6. Acerate spicule (upper) x 210, and acuate spicule (lower) 

 X 260. 



Jonrn. QmUtt Microscopical Ch'.b, Ser. 2, Vol. VII., No. 46, April 1900. 



