70 I. IJIMA : HEXACTINELLIDA. I. 



of 10-30/^ and more near the spicular center. The rays are 

 for the greater part of nearly uniform thinness ; the ends are 

 slightly swollen and rough, the extreme tip being either rounded 

 or bluntly conical. The unilateral ray may be of considerable 

 length (up to 15 mm.) but more often it is relatively very short, 

 being sometimes only 1 mm. or even less in length. It sticks 

 out of the skeletal beams nearly vertically at indefinite positions 

 and in all directions. Among the comitalia I have on rare 

 occasions met with fine diactins in which the suppressed rays 

 were represented by mere knobs at the center. 



The longitudinal skeletal beams may attain a thickness of 

 over 1 mm. The transverse beams are on the whole somewhat 

 thinner. 



The oblique beams of the skeletal framework consist, unlike 

 those of the two other systems, almost entirely of thetactins which 

 are however quite similar to those just described. Some of these 

 thetactins may here be of moderate strength (up to 100 a in 

 thickness) and may be regarded as representing the principalia 

 of the beams. Sometimes such stronger elements were found to 

 be oxydiactins. 



The spicules of the skeletal beams above referred to begin to 

 undergo synapticular fusion in the well-known manner at the 

 lower end of the body and that at a time when the sponge has 

 acquired a height of about 200 mm. With further growth, the 

 soldering gradually extends upward to about the middle of the 

 body but probably never further than that ; for, even in the 

 largest specimen (X) before me, I find all the spicules in the 

 upper, half in loose association with one another. Here seems 

 to exist another point of difference from the closely allied 

 E. regalis F. E. Sen., in which the soldering j^rocess appears to 



