158 THE VOYAGE OF H.M.S. CHALLENGER. 



Piocamia coriacea, Bowerbank, sp., var. elegans, nov. (PI. XXIX. fig. 9 ; PI. XXXI. 

 fig. 1). 



1874. Isodidtja coriacea, Bowerbank, Mon. Brit. Spong., vol. iii. p. 228, pi. Ixxvi. figs. 7-12. 

 1881. Dirrhopalum coriaeeum, Ridley, Joiu'ii. Linn. Soc. Lond. (Zool.), vol. xv. p. 481 



pi. sxix. figs. 3-7. 

 1886. Piocamia coriacea, var., Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 475. 



A single, small, dichotoinously branched specimen (PI. XXXI. fig. 1) of the form 

 shown in the figure. Total height 38 mm. ; diameter of branches, which are cylindrical, 

 about 2"5 mm. Colour in spirit pale yellow. Texture soft and spongy. Surface even 

 and minutely hispid. Dermal membrane very thin, delicateand transparent. Oscula 

 and pores unknown ; the sponge is apparently lipostomous. 



Skeleton. — A close but irregular Isodictyal reticulation of the characteristic sausage- 

 shaped spicules of the genus ; amongst these, towards the surface, one distinguishes 

 radiating lines of smooth stylote spicules, which terminate in free, projecting brushes, 

 causing the hispidity of the surface. 



Spicules. — (a) Megasclera; of three very distinct kinds, (l) («) Fairly stout, 

 slightly curved, smooth styli, with sharp points and evenly rounded bases (which are rarely 

 or never spined, and difi"er from those of the type in this respect); above the base 

 there is a slight constriction; these spicules vary much in size, averaging about 0"5 by 

 0"0126 mm.; they occur in the primary , radiating lines, from whose ends they freely project. 

 (/S) Very much slenderer, sharply pointed, straight subtylostyli, measuring about 0'3 by 

 0-003 mm., abundant in tufts on the surface, scattered through the dermal membrane, &c. 

 (2) Curved, stout, entirely spined, sausage-shaped spicules (PI. XXIX. fig. 9), with a 

 slightly developed head at each end, which bears more numerous but perhaps smaller 

 spines than the shaft; size about O'll by 0*0094 mm. This is the most abundant and 

 characteristic spicule, it forms the Isodictyal reticulation above mentioned. (3) Entirely 

 but slightly spined, slightly curved styli, narrowing towards the base, which bears more 

 spines than the shaft; measuring about 0*18 by 0'0094 mm.; only fairly abundant, 

 echinating the radiating, main filn-es near the surface. (6) Microsclera ; of two kinds. 

 (1) Small, palmate isochelae, length about 0*019 mm., very abundant in the dermal 

 membrane, but not so common in the deeper parts of the sponge ; (2) very numerous, 

 slender toxa, with minutely spined ends, varying considerably in size, full grown 

 examples being about O'l mm. long. 



Bowerbank's species was, in the first instance, very imperfectly described, but it will 

 be seen by reference to Ridley's description and figures [loc. cit.) that in the arrangement 

 of the skeleton and the form and proportions of the various spicules the Challenger 

 variety comes very near to it. The main diff'erence in spicular measurements concerns the 

 toxa, which seem to attain a greater size in Bowerbank's sponge than they do in ours. 



