TETRAXONIDA. 5 



Spicules. Megascleres. 1. Large oxeas, 9 • 7 x 0" 081 mm. 



2. Smaller oxeas, scattered in the choanosome, 540 to 1350 jn in length. 



3. Cortical oxeas (XL 8), 770 x 30 n, straight, fusiform. 



4. Anatriaenes of three kinds: a. (XL 9) Cladi 170 jn long x 20 fi thick at 

 base, slender, sharp-pointed, chorda 110 /i; rhabdome, about 12 mm. long, thick at 

 junction with cladome, then tapering, again thickening, and finally terminating in a 

 filiform extremity. 



b. (XL 11) Cladome with thick conical cladi, 140 x 35 fi, chorda 60 yu,; rhabdome 

 with a thick neck, and then nearly uniform till it tapers to a filiform extremity. 



c. (XI. 10) Cladome with very long, straight, slender cladi, 150 X 10 fX, nearly 

 parallel with, or making an angle of, about 10° with the rhabdome, chorda only 31 /a ; 

 rhabdome slender (of uncertain length) . 



5. Protriaenes. Eare, usually with three slender equal cladi, 90 /a long ; rhabdome 

 of nearly uniform diameter ; but slightly diminishing near the cladome. 



6. Trichodal protriaenes, usually (especially in the case of those forming the inner 

 oscular fringe) with one ray greatly prolonged to 140 fi or more, the other two having 

 almost disappeared ; rhabdome slightly thickened at cladal origin. 



7. Sigmata, 14-25 to 15 n long, 0'75 /x thick, and 12"3/i broad in the c aspect, 

 with slightly and finely granulated surface. 



There are three specimens of this sponge, the largest (XL 4) being 12 cm. 

 in total length and 5 • 2 cm. in breadth, with a root-tuft 3 * 5 cm. in length ; 

 the second specimen (XL 5) is oval, 2' 9 cm. long and 1'7 cm. broad, and the smallest 

 is 13 X 12 mm. 



The colour of the first two is dirty gray, and that of the last pale buff. 



The scale-like, occasionally over-lapping, verrucae, attain a height of 2 mm., and 

 a breadth at the base of 4 mm. 



The oscule is oval-shaped, edged with a barely visible fringe of trichodal 

 protriaenes ; it measures, in the large specimen, 7 • 5 x 5 mm. 



The skeleton. The radiating fibres only very rarely project beyond the surface ; 

 near the oscule are a few tufts of oxeas. Over the rest of the surface of the sponge, 

 the dermal membrane covers over the summits of the verrucae, the distal points of 

 oxeas and the cladomes of anatriaenes showing through ; medium-sized in large 

 protriaenes, so abundant in Craniella sagitta, are almost absent from the two large 

 specimens of the present species, though in the smallest specimen there is one to each 

 conule. Tufts of trichodal protriaenes are present in abundance. 



The ectOSOme. On section, the ectosome is scarcely difierentiated from the 

 choanosome, excepting that sub-dermal spaces are visible just beneath the dermal 

 membrane. 



The cortical oxeas are more densely packed than in the preceding species. 



A tangential section shows the pores in longitudinal areas between the densely 

 serried rows of cortical oxeas, and fan-like tufts of trichodal protriaenes supporting the 



