8 AKT. 9. — I. IJIMA : HEXACTINELLTDA. 



gradually in size down to such small and slender-rayed oxy- 

 hexactins as measure only 100,« or under in axial length and 

 about 3 fi in breadth of ray near the center. These may be 

 culled microxvhexactins. They occur in scattered distribution, 

 though at places several may be found side by side. There are 

 to be distinguished two kinds of the microxyhexactin, viz., the 

 smooth (PL, fig. 8) and the spiny (PL, fig. 9). 



Of these the spiny microxyhexactin is more numerous and 

 certainly more highly characterized. The rays are not in- 

 frequently of unequal length in the same spicule ; they are either 

 nearly straight or slightly bent. Except in the basal part, each 

 of them is supplied with a varying number of rather slender 

 spines (up to 7 /^ in length). These are irregularly distributed, 

 and indefinite as to their direction, being sometimes recurved, 

 sometimes obliquely outwardly directed and at other times pro- 

 jecting nearly vertically. Their number on a ray may be quite 

 small, sometimes even only two or three. In certain cases the 

 few spines present were quite obsolete, a fact which seemed to 

 indicate a gradational transition between the spiny and the smooth 

 microxyhexactins. Axial length of the spiny microxvhexactins 

 generally 120-130/;, exceptionally 280 p. Similarly spinose mic- 

 roxyhexactins occur also in C. clegans, C. pulchra, Regadrella 

 ohinoseana and Diclyaidus elegans, and further in a peculiarly 

 modified form in Hcterotella corbicula. 



Of a somewhat doubtful nature are the small, thick-rayed 

 spicules of stunted appearance, which are met with in some 

 numbers in certain parts of my preparations (PL, figs. 5-8). 

 They are usually pentactins but occasionally a hexactin, a tauactin 

 or a compass-needle-like diactin. The stout-looking rays are 

 smooth, nearly uniformly broad throughout, and with rounded 



