120 
THE VOYAGE OF H.M.S. CHALLENGEE. 
Remarks. — There is but a single specimen of this sponge in the collection ; it measures 
14 mm. in length by 11 mm. in breadth. 
Its resemblance to Myriastra clavosa is so considerable that I should have included 
it in that species, but for the larger size of the cladome of the anatrisene, and the 
thickening of the rhabdome of the dichotrisene below the cladal origin. This latter 
character would not alone appear to be of much importance, but since it appears very 
early in the development of the spicule, giving to it a striking and unusual appearance, 
very different from that of the young forms of the corresponding spicule in Myriastra 
clavosa, I am disposed to set some value on it. The chiasters are also distinguished by 
slight differences, the actines are usually thicker and fewer in number, reductions to three- 
or even two being frequent ; the tylote terminations are also better developed, and 
sometimes become subdivided into three or more rounded lobes. The ectosome is 
0‘3 mm. thick; the flagellated chambers 0'024 by 0'016 mm. in length and breadth, 
they are frequently eurypylous ; the apopyle measures about 0*0 16 mm. in diameter. 
Genus 2. Pilochrota^ Sollas. 
Oscules usually distinct. Pores in sieves leading into radial incurrent canals, which 
are not constricted on passing through the fibrous layer of the cortex. Ectosome differ- 
entiated to form a cortex, which usually consists of a middle collenchymatous layer, an 
outer thin fibrous layer and an inner thicker fibrous layer. The microsclere is a chiaster. 
Pilochrota haeckeli, Sollas (PI. XIV. figs. 1-8). 
Pilochrota liaecheli, Sollas, Prelim. Account, Sci. Proc. Roy. Dul)l. Soc., vol. v. p. 189, 1886. 
Sponge (PI. XIV. fig. 1). — Subglobular ; attached to it are numerous foreign bodies, 
which are most abundant around the oscule.’^ The oscule is single, oval, and with a 
smooth, thickened, membranous margin ; it leads into a large cloaca, the sides of which, 
close to the oscule, are hispid with minute, projecting, oxeate spicules. The surface is 
rough, the poriferous sieves being situated in pit-like depressions surrounded by non- 
poriferous ridges, into which the radiating spicules of the interior enter. 
Spicules.— 1 . Megascleres. 1. Somal oxea (PI. XIV. fig. 2), stout, fusiform, 
usually curved and sharply pointed, 2'07 by 0'046 mm. 
2. Cloacal and ectosomal oxea, small fusiform, sharply pointed, 0'2 by 0’004 mm. 
3. Orthotrisene (PI. XIV. fig. 3), rhabdome conical, stout below the cladome, 
rapidly attenuating to an almost filiform extremity, extremely sharply pointed or 
^ Tci’ho; 0 , felt ; ® skin. 
2 In the illustration the sponge is represented with the surface hearing the oscule (which is not shown) turned 
downwards. 
