Spongillidae. 239 



Sporigilla nitens has hitherto been found in tlio "White Xile and in 

 the neighbourhood ofLake Tanganyika. 



Spongilla niichaelseni, sp. nov. 



PI. VI, Üg. 3 A-C. 



Sponge encrusting, forming thin Hat lilms of limited area and of a 

 greyish colour; moderately hard, friable, brittle. Oscula and pores minute, 

 inconspicuous. Subdermal space relatively small. 



Skeleton formed of slender, well-delined but not very coherent 

 radial spieule-fibres joined together by an ii-regular network of spicules 

 that exhibit little evidence of fascieulation; little spongin present. 



Spicules (PI. VI, Fig. 3): Skeleton-spicules perfectly smootli, sharply 

 and gradually pointed at both ends, feebly curved, on an average about 

 23 times as long as thirk. Free microseleres slender, .'^traight or nearlv 

 so, sharply and gradually pointed at both ends, bearing numerous sharp 

 spines that stand out straight at right angles to the siu-face and are mueli 

 larger in the middle of the spicule (while they are often as long as the 

 shaffc is wide) than at the ends. Genimule-spicules verv variable in size, 

 spiny, ampliistrong^dous, moderately stout: their spines as a rule longer 

 and more numerous at the ends of the spicule than in the middle (where 

 they are sometimes almost absentj, often distinctly reeurved at and near 

 the former, very variable in length; a single terminal spine often present 

 at one or both extremities. 



Gemmules somewhat depressed, small, pro\ided \\\t\\ a thick coat 

 of well-developed polygonal air-spaces and with a straight and rather stout 

 foraminal tubule, which Stands upright in a crater-like depression of the 

 pneumatic eoat; spicules arranged both tangentially and horizontally in this 

 coat, forming a somewhat ill-defined horizontal layer on its exfernal surface. 



Diameter of gemmide ca. 0.42X0-36 mm 



Length of skeleton-spicule 0.308—0.356 „ 



Tliickness of skeleton-spicule 0.012 — 0.017 ,, 



Length of free microsclere 0.068 ,, 



Thickness of free microsclere (shaft) . . 0.004 ,, 



Length of gemmide-spicule 0.076 — 0.156 ,, 



Tliickness of gemmule-spicule (shaft) . . 0.005 — 0.016 ,, 



This species is related to Spongilla carteri, the commonest of the 

 Indian Spongillidae, but distinguished by possessing free microscleres and 



