42 ART. 7. T. IJIMA : HEXACTINELLIDA, lY. 



bread tli of rays at base between 7 // and 12 I'-. On the mem- 

 branons oscular margin the size may decrease to 264 fj. axial 

 length. Exceptionally slender-rayed dermalia, found occasionally 

 by the side of stouter ones, represent without doubt a develop- 

 mental stage preceding the attainment of definitive dimensions. ' 

 The dermalia are found irregularly scattered in the dermal 

 membrane. They can not be said to l)e numerous; in many 

 places they occur in no greater, if not in somewhat smaller, num- 

 bers than the hypodermalia. Altogether, it may be said that the 

 latter with their paratangentials are about as much concerned in 

 the support of the dermal membrane as are the dermalia them- 

 selves. (See PI. III., fig. 10. In this figure, the cruciate spicules 

 di^awn in blue represent partly the dermalia and partly the 

 paratangential crosses of the hypodermalia. Through the deeply 

 stained dermal membrane, perforated by roundish gaps or pores, 

 is seen the most peripheral part of the choanosome). 



The gastralia are represented l\v both hexactins and pentact- 

 ins, the latter having the unpaired ray directed distad. I can 

 not definitely state which of the two forms j^i'edominates, though 

 in some places I have found several of the former form placed 

 together side by side. In any case the gastralia are on the whole 

 rather sparsely present, l)eing situated in isolated positions. The 

 rays are similar in appearance to those of the dermalia ; their 

 length as msasured from the spiciilar center is 165-176 ft. 



The hexasters are of the following two kinds : 



Common but not alnnidant are tlie oxyhe:(-aslers (PI. III., 



fig. o) in the choanosome as well as in the subdermal space. 



They are characterized by the possession of rather numerous 



