Marine Sponges from Japan. 397 



tose sponges, in which the branches are tubulo- digitate and 

 open at the ends, as in the tubulo -digitate Chalinse; also, 

 although in a minuter form, to the clathrotubular structure 

 of the Calcareous sponges Clathrina, and the carneous Hali- 

 sarca lobularis. 



Hexactinella ventilabrum, n. sp. (PI. XIV. figs. 1-10.) 



Specimen, a large undulating somewhat compressed bowl, 

 with irregularly plicated sides, approximated towards the ends 

 and into a keel below ; very thin wall and contracted sub- 

 stipitate point of attachment ; 1\ inches high, 13 inches long 

 horizontally and 8 inches across the most open or central part 

 of the brim, which is rendered very irregular by its deep sub- 

 plicate undulations ; sides chiefly approaching each other 

 towards the ends, which, not being actually united, are thus 

 rendered rimous ; base keel-shaped, owing to the angular 

 approximation of the sides at the bottom, descending sub- 

 funnel-shaped to the stem, which is excentric, about 1^ in. 

 in diameter, spreading out afterwards for attachment. 

 Consistence firm, vitreous. Colour transparent white. 

 Surface on both sides even and uniform ; uniformly scattered 

 over internally with circular apertures about j 2 - in. in diameter 

 and about the same distance apart (PI. XIV. fig. 1), and 

 externally with a dermal, quadrilateral, spicular reticulation, 

 in the interstices of which the sarcode, although dry, is pre- 

 served (fig. 2, a). Vents on the inner side of the bowl, viz. 

 the "apertures" just mentioned (fig. 1). Pores in the sar- 

 code tympanizing the interstices of the dermal reticulation, 

 about 1000th inch in diameter, more or less (figs. 2 and 9). 

 Wall about l-6th in. thick, composed of two layers, viz. one 

 on each side of an irregular central plane of condensed tissue ; 

 each layer consisting of plumose fibre curving upwards and 

 outwards florally from the central plane to the respective 

 surfaces, strengthened by transverse fibres in their course 

 (figs. 3 and 8) j the whole, when the flat surface is placed 

 between the observer and the light, presenting a fibrous, 

 vertical, linear reticulation, formed by condensed tissue in the 

 interior. Loose spicules of seven forms, that is including the 

 skeletal fibre (fig. 4, «-</), viz. : 1, dermal sexradiate, with 

 outer ray aborted and reduced to a round knob ; arms 

 and shaft gradually diminishing towards the free ends, 

 which are abruptly pointed ; knob and rays microspined 

 throughout (fig. 4, g) ; ray about 25 by 2-1800ths in. in its 

 greatest dimensions, but variable. 2, the barbula (see PI. XIII. 

 tig. 3). 3, smooth acerates, more or less flexuous from their 



