182 
THE YOYAGE OF H.M.S. CHALLENGEK. 
Astrella dordgera (0, Schmidt). 
Stelletta clorsigera, 0. Schmidt, Spong. Adriat. Meeres, Suppl., p. 31, 1868. 
Sponge. — Spherical, surface raised into very irregular conules ; pores large, in sieves, 
cortex thick, differentiated into a cavernous outer half and a dense fibrous inner half, 
containing a few grains of sand and other foreign bodies scattered through it. Outer ends 
of the chones enlarged into wide cavities into which the, pores open ; inner ends conical, 
constricted into narrow canals, which open into the subcortical crypts. 
Spicules .' — I. Megascleres. 1. Oxea, fusiform, sharply pointed, 3‘0 by 0’06 mm. 
2. Orthotrisene, rhabdome conical, sharply pointed or strongylate ; cladi conical, 
sharply pointed. Rhabdome 1*6 by 0*06 mm., cladi 0*127 mm., chord 0*223 mm. long. 
II. Microsclere. 3. Chiaster, centrum very small, actines cylindrical, strongylate 
or truncate, varying in number from four to many; average diameter 0*016 mm., forms 
with four actines only, as much as 0*024 mm. in diameter. These asters form a layer 
beneath the epithelium, and are distributed generally throughout the sponge. 
CoZowr.— Blackish-brown externally, greyish- white within. 
Habitat.-^ljesma, in the Adriatic Sea. 
Remarks . — At first I assigned this sponge to the genus Psammastra, but since it 
does not contain the characteristic microstrongyle, I am now inclined to regard it as an 
aberrant form of Astrelloj, from which it differs chiefly in possessing conules. These, 
however, are different in character from those of Psammastra murrayi, being much 
more irregular. The orthotrieenes are subject to modifications somewhat similar to those 
of the last-named species ; thus they are frequently reduced to oxystrongyles and oxyty- 
lotes, the latter usually retaining their trisene character by a branching of the axial fibre ; 
the former usually not, but yet frequently indicating their origin by the presence of 
one or more cladi irregularly given off some distance below the strongylate end ; in 
one instance an oxystrongyle was observed bearing a single normal dichocladus. 
The pores are large, varying from 0*0326 to 0*1 mm. in diameter. 
Astrella pumex (0. Schmidt). 
Stelletta pumex, O. Schmidt, Spong. Adriat. Meeres, Suppl., p. 32, pi. hi. fig. 9, 1864. 
Sponge. — Irregularly incrusting, surface hispid. 
Spicules. — I. Megascleres. 1. Oxea, 2*13 by 0*044 mm. to 2*7 by 0*06 mm. 2. 
Plagiotriaene, rhabdome 1*43 by 0*055 mm., cladus 0*286 mm. long. 
II. Microsclere. 3. Pycnaster, small and variable in form, passing into oxyasters, 
spherasters, and chiasters without change of size, 0*019 mm. in diameter. 
Colour . — Blue-black externally, yellowish-white within. 
Habitat . — Venetian Canal. 
