■REPORT ON THE MONAXONIDA. 105 



Desmacidon reptans, Ridley and Dendy (PI. XXIII. figs. 7, 7a, 7h). 



1886. Des7naculon reptans, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 345. 



Sponge encrusting, creeping over other sponges of different species, or free ; massive, 

 amorphous, or digitate. Colowr in spii-it greyish-yellow. Texture fairly firm, 

 resilient. Surface glabrous-looking, but slightly rough to the touch, marked with 

 shallow and for the most part longitudinal grooves. Dermal membrane thin and 

 delicate. Oscula small, scattered. Pores small, scattered. 



Skeleton. — (o) Dermal; varying in its degree of development according to the 

 particular specimen examined. Sometimes it is composed of a comparatively wide- 

 meshed reticulation of stout fibre, composed of broken spicules and foreign bodies, while 

 the polygonal meshes of this network are again filled in by the much smaller polygonal 

 meshes of a finer network, composed of more slender fibre, but of the same character. 

 The meshes of the finer reticulation are only about 0'07 mm., while those of the coarser 

 reticulation may be 0'35 mm. in diameter. The finer reticulation appears to be at a 

 slightly higher level than the coarser one. At other times the two reticulations are not 

 distinguishal^le from one another, the whole dermal skeleton is more irregular, and the 

 foreign bodies are in great part or entirely replaced by the proper oxeote spicules of the 

 species ; while again at other times the number of foreign bodies present in the fibres may 

 be very great, consisting chiefly of sand grains. (6) Main ; an irregular, fairly close, 

 somewhat Isodictyal reticulation of oxeote spicules, often several lying parallel side by 

 side, but rarely united into distinct fibres. 



Spicules. — («) Megasclera ; of one kind only, viz., smooth oxea (PI. XXIII. figs. 7, 

 7a), tapering rather abruptly to a sharp point at each end; size about 0'18 by 

 0-008 mm. (b) Microsclera ; of two kinds; (l) isochelse (PI. XXIII. fig. 7b), with 

 three sharp teeth at each end, length about 0'019 mm., rather rare ; (2) numerous 

 simple or contort sigmata, about 0'038 mm. long. 



In spiculation this species comes near to Desmacidon fruticosa, Montagu, sp., the 

 type of the genus.-^ It difi"ers, however, in the much slighter development of horny 

 matter in the fibre, and in tlie much smaller size of the chelate spicule (0'032 mm. 

 long in Desmacidon fruticosa as against 0"019 in Desmacidon reptans). The habit 

 appears also to difi'er considerably. 



The sponge afi"ords a good example of the way in which foreign bodies may replace 

 the proper skeleton, being arranged along the true skeleton lines. 



Locality. — Ofi" Bahia, shallow water ; two specimens. Off Bahia ; 7 to 20 fathoms ; 

 three specimens and some pieces. 



' Cf. Bowerbank, Mon. Brit. Spong., vol. i. p. 200, &c. 



(ZOOL. CHALL. EXP. — PART Lix. — 1887.) Nnn 14 



