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



Spicules. — Large, stout, fusiform oxea (PI. II. fig. 9), curved, and gradually and 

 fairly sharply pointed ; size about 0'45 by 0*028 mm. 



This species is at once distinguishable from all others of the genus by its external 

 form and its characteristic chitinous envelope (hence the specific name). The size and 

 shape of the spicules are also very characteristic. In the presence of an external 

 chitinous membrane it resembles Rhizochalina Jistulosa. Like the preceding species, it 

 has a great general resemblance to Petrosia, but, on the other hand, the skeleton 

 arrangement shows some approach to the rectangular character of Reniera; but as the 

 dermis is subreticulate, and the spicule is a large tapering oxeote, it seemed best 

 to regard it as a decidedly aberrant member of the genus Halichondria. 



Locality. — Amboina ; depth, 100 fathoms. One specimen. 



Halichondria latrv,nculioides, Ridley and Dendy (PI. I. figs. 5, 5a ; PI. II. 

 fig. 1 ; PI. XLVI. fig. 5). 



1886. Halichondria latruncuUoides, Eidley and Dendy, Ann. and Mag. Nat. Hist., .ser. 5, 



vol. xviii. p. 326. 



Sponge erect, lobose ; two out of the three specimens collected are pear-shaped, and 

 have apparently been attached by the narrow end to the substratum on which they grew. 

 The third specimen, which is the largest, is lobose and compressed in a vertical plane ; 

 it has a much constricted base, by which it has evidently been attached. The largest 

 specimen measures 44 mm. in height, by 72 mm. in greatest breadth, and about 12 mm. 

 in average thickness ; the larger of the two pear-shaped specimens measures 50 mm. in 

 height by 27 mm. in diameter near the top. Colour in spirit light grey. Texture 

 rather soft and spongy internally. Surface uneven, deeply corrugated, but glabrous ; 

 with numerous large, round or oval, flat, sieve-like pore-areas, elevated above the general 

 surface of the sponge, and constituting by far the most important character of the 

 species (PI. I. fig. 5, p.a., and fig. 5a). Dermal membrane forming (except in the pore- 

 areas), together with its supj^orting layer of spicules, a thickish, parchment-like crust, 

 readily separable from the underlying tissues. In the pore-areas, on the other hand, 

 the dermal membrane is very thin, delicate, and transparent, and reduced to a mere 

 sieve by the very numerous pores. Oscida at the summits of conical projections of the 

 parchment-like dermal membrane at the top of the sponge (PL I. fig. 5, o). Pores 

 almost entirely confined to the pore-areas (PI. I. fig. 5a) ; we have, however, detected a 

 few in gaps in the almost continuous dermal skeleton. 



Skeleton. — (a) Dermal ; a very dense, in most parts perfectly continuous layer of 

 large oxeote spicules laid horizontally side by side (PL XLVI. fig. 5). {h) Main; 

 loose, composed of rather irregularly arranged spiculo-fibre ; the fibre itself is often 

 fairly stout, but not very definite or compact. 



