ON SOME JAPANESE CALCAREOUS SPONGES. 25 



The tubar skeleton is of the inarticnlate type, being composed 

 of the strong basal rays of subdermal pseudosagittal triradiates as 

 well as of subgastral sagittal triradiates of varying sizes, respect- 

 ively directed centripetally and centrifugally. 



The gastral skeleton is thinner than the dermal. It is com- 

 posed of the strong paired rays of subgastral sagittal triradiates, 

 and of sagittal triradiates which are similar to those of the dermal 

 skeleton except in being slightly smaller and rather more regularly 

 arranged. 



The skeleton of the oscular margin is composed of oxea and 

 triradiates, both placed densely together. The former run longi- 

 tudinally and parallel with one another, the latter have strongly 

 divergent paired rays. 



Spicules. 



Dermal triradiates (textfig. 5, a, h). — Subregular or slightly 

 sagittal, varying in size. All rays conical, nearly straight, often 

 slightly irregularly contoured, tapering from base to sharply 

 pointed end, 130-410,« long and 20-50;« thick. Towards the 

 osculum the triradiates become distinctly sagittaUy differentiated. 



Subdermal triradiates (textfig. 5, c, d). — ^Pseudosagittal, irregu- 

 lar, strongly developed. All the rays differing in length, some- 

 what irregular in contour. Basal ray almost straight, tapering 

 from base to sharp point, occasionally slightly thicker than paired 

 rays, 320-630 /^ long and 30-60 ,« thick. Paired rays are equal 

 in thickness, but unequal in length and shape. The longer ray 

 usually curved, sometimes crooked, gradually tapering, 160-430/^ 

 long and 30-50 /^- thick. The shorter ray less curved than the 

 longer, gradually pointed, 120-330 ß long and 30-50 « thick. 



Subgastral triradiates (textfig. 5, e,f). — Strongly sagittal. On 



