21(3 THE VOYAGE OF 11. M.S. UHALLENGEfl. 



Spicules. — Megasclera; (1) small, slender, very slightly curved, sharply and gradually 

 pointed tylostyli (PI. XLII. figs. 8^, 8/i) with not very well-develoj)ed oval heads, size about 

 0"16 by 0"0045 mm.; these spicules occur in the outermost layer of the cortex. (2) Much 

 larger, very stout, sharply pointed, fusiform tylostyli (PI. XLII. figs. Be, 8/), with roundish 

 heads ; size variable, about 0"22 by 0"0189 mm.; occurring in the lower cortical layer and 

 passing gradually by spicules intermediate in form and size into (3) the long styli (PI. XLII. 

 fig. 8) of the fibres ; these are smooth, straight, fusiform and sharply and gradually 

 pointed at the apex; size about 1'2 by 0'03 mm. (4) The grapnel spicules (PL XLII. 

 figs. 86, 8c, 8rf); long, very slender, with more or less expanded base and tapering very 

 gradually to hair-like fineness towards the apex, ending finally in a small knob provided 

 with recurved teeth which do not seem to be quite constant in number ; commonly there 

 are about four teeth, but owing to the minute size it is not easy to make out details; 

 sometimes the teeth are absent, leaving only the knob. Length of spicule about 

 0"52 mm., thickness at thickest part of shaft about 0'0063 mm. 



Locality. — Simon's Bay, Cape of Good Hope; depth, 10 to 20 fathoms. One 

 specimen. 



Genus Trichostemma, M. Sars (PI. XLIIL). 



1872. Tricliostemiiia, M. Sars, Eemarkable Forms of Animal Life, pt. i. p. 62.' 

 1870. Radiella, Schmidt, Spong. Atlant. Gebiet., p. 48 (not Radiella, Sollas, Ann. and JNlag. 

 Nat. Hist., ser. 5, vol. ix. p. 162). 



Sponge free living, with definite, symmetrical, external form ; discoid or hemi- 

 spherical ; with a marginal fringe of long, hair-like spicules serving to maintain the 

 sponge in its position in the mud. Oscula, one or more at the ends of short oscular tubes 

 on the upper surface. Megasclera mainly tylostylote. 



The original diagnosis {Joe. cit., p. G5) runs : — " Spongia silicea, simplex, libera, in limo 

 demersa et hie fimbria spiculorum setiformium, fiexibiHum, radiantium sustentata, corticc 

 crasso compacto circumdata, iuteriore multo minus compacto, parenchymatoso, lacunis 

 numerosis irregularibus trajecto. Oscula numerosa tubiformia in facie superiore libere 

 prominentia. Sceletum ex spiculis acuformibus fasciculato-radiantibus compositum, aliis 

 brevissimis capite globoso in cortice densissime accumulatis, aliis multo longioribus. 

 fasciculos tenues parenchyma et corticem trajicientes formantibus. " 



The original type of the genus is Trichostemma hemisphiericum, Sars, which " occurs 

 not rarely at Lofoten .... in a depth of 120-300 fathoms on soft clay bottom." The 

 Challenger adds two new species, both from a very great depth and a bottom of ooze or 

 mud. It is essentially a deep-sea genus, and forms another example of the manner in 

 which deep-sea sponges commonly assume a definite, symmetrical external form ; in this 



' The gonus and species are first described in this place as nov. gen. et spec, but the name is used by Sars so far back 

 as 1869 (Forhaiidl. Vitleiisl: Selnk. Cliristiania, 1869, p. 250), without, however, any doscriptionj 



