240 I. IJIMA : HEXACTINELLIDA. I. 



of young specimens which I refer to the present species, not- 

 withstanding certain discrepancies between them and the adult 

 forms in both nnicroscopical and microscopical respects. The 

 series comprises different stages, from one in which the body is 

 smaller than a grain of rice to such as have the characteristics 

 of the adult nearly completely developed. The specimens will 

 here be described in the order of their development, beginning 

 with the youngest. 



1. On two stumps of dead skeletons (Mus. Xos. 309 & 370), 

 which I have identified as H. okinoseana from microscopical 

 examination of their spicules and both of which were obtained 

 from Inside Okinose during January, 1895, were found several 

 small and delicate Hexactinellids of a club-like or elongate ovoid 

 shape. They were attached by a small basal expansion at the 

 narrowed lower end to the beams, on both the inside and out- 

 side of the dead specimen. The smallest individual of the lot 

 was only 4 mm. long with a breadth of about 2 mm.; the largest, 

 13 mm. by G mm. In PI. YII, fig. o are shown three of the 

 small specimens in question, magnified about V/._> times. The 

 rounded upper end always shows a simple, round or oval oseulum 

 which leads into a deep, tubular, gastral cavity. The dermal 

 surface is smooth and nowhere interrupted by parietal gaps. 

 Thus, in macroscopic respects, the specimens can scarcely be 

 distinguished from those of either Vitrollula or Leucopsacin^ ; and 

 even after gaining a knowledge of their spiculation, I was at 

 first far from recognizing them to be the young oî E. okinoseana, 

 the same in species as the dead sponge to which they were 

 attached. 



In the first place, the dermalia (PI. VII, figs. 8, 10, 11) are 



