REPORT ON THE MONAXONIDA. 169 



Skeleton. — The main skeleton consists of a dense but quite irregular reticulation of 

 large stylote spicules, the spicules occasionally lying side by side in loose tracts. At 

 the surface there is a thin crust of similar large styli, also densely and very irregularly 

 reticulate and giving support to numei'ous small stylote or subtylostylote sjaicules, 

 which project more or less vertically outwards ; we have never found these small 

 projecting spicules forming a very dense crust, though in some parts they are very 

 abundant ; it is doubtful whether the layer of large styli on which they rest should be 

 regarded as anything more than the uppermost part of the main skeleton. 



Spicules. — Megasclera; (l) very large, stout, smooth, fusiform styli (PL XL. figs. 

 5, 5a), more or less curved or slightly crooked ; tapering fairly gradually to a sharp 

 point at the apex and tapering rather suddenly near the base to a very narrow neck ; 

 the base is evenly rounded off at the extremity, and is often so narrow that 

 the spicule becomes nearly oxeote in appearance, but we have never found the base 

 pointed, always rounded off; size about 1'2 by 0"031 mm. (2) Small, slender, nearly 

 or quite straight, gradually and sharply pointed styli or subtylostyli ; not markedly 

 narrowing towards the base ; size commonly about 0"2 by 0"0063 mm. The mode of 

 occurrence of these two forms of spicules has been noted above. 



This species would probably have been included by Mr. Carter in his genus 

 Leucophlasus, but we are unable to discern any tangible and constant character wherebj' 

 the latter genus may be separated from Hymeniacidon. 



One of the most characteristic features of our present species is the shape of the large 

 stylote spicule, which is very peculiar ; it demonstrates that a stylus might readily give 

 rise to an oxeote spicule. The narrowing towards the base of the spicule may also be 

 seen, though not carried to the same extent, in Leucophlceus fenestratus, Ridley,' 

 especially in one of the varieties. The small surface spicule appears to occur in Leuco- 

 jMceus fenestratus also (though not described), but is much stouter there. In Leuco- 

 phloeus proteus,^ Ridley, it appears not to occur, and the large spicule has an 

 ordinary broad, rounded base. The external form of Hymeniacidon (?) subacerata is 

 quite different from that of Leucophlceus fenestratus. 



Locality.— Station 208, January 17, 1875; lat. 11° 37' N., long. 123° 31' E.; 

 Philippine Islands; depth, 18 fathoms; bottom, blue mud. Three specimens. 



Genus Phakellia, Bowerbank (Pis. XXXIV., XXXV., XXXVL, XL.). 



1864. Phakellia, Bowerbank, Mon. Brit. Spong., vol. i. p. 186, &c. 



Sponge more or less flabellate or cup-shaped. Skeleton often more or less reticulate. 

 Megasclera styli and often oxea. No microsclera. 



1 Zool. Coll. H.M.S. "Alert," Brit. Mus., 1884, p. 4G4, pi. xlii. fii;. s. 



2 Op. cit., p. 620, pi. liii. fig. B ; pi. liv. fig. k. 



(zOOL. CHALL. E.XP. — PART LIX. — 1887.) Nim 22 



