232 I. IJIMA : HEXACTINELLIDA. I. 



meslies. In addition to the same megascleric elements as are found 

 in the upper part of the skeleton, there are contained in the basal 

 mass a large quantity of peculiar hexactins, which occur nowhere 

 else and which I have called the hasidictyonalia. The hexactins 

 in question are comparatively small in size but have thick, plump- 

 looking rays, which are nearly smooth or show a few microtubercles 

 near their rounded ends (PI. YIII, fig. 34). The basidict3'onalia 

 are at first loose but soon become soldered to the general framework 

 of the region. PI. X, fig. 17, representing a small piece of the 

 basal mass taken from 11. homeyamal, may just as well pass for 

 the same of the present species ; in it some of the beam nodes 

 are plainly the center of basidictyonal hexactins. The secondary 

 deposit of siliceous matter over the surface and the synapticula3 

 irregularly proceeding from it often make the hexactins unre- 

 cognizable as such externally, but the characteristic triaxial 

 central filaments remain in the beams. 



The basidictyonalia seem to be of quite general occurrence 

 among those Lyssacine Hexactinellids which are attached to hard 

 foreign bodies directly by a part of the wall, and whose sj^icules 

 undergo extensive ankylosis in the basal region. F. E. Schulze 

 figured them from the firm stalk of Cratcromorpha meyerl (Chall. 

 Kep,, pi. Lxr, figs. 5 & G). To them I refer also the rigid 

 reticulum of spicules described by the same writer ('gg, p. G4) 

 from the buds of Rhahdocalyplus mirabilis, which fact I have al- 

 ready had occasion to mention on p. 186 (foot-note). And, I shall 

 have to demonstrate their presence in a series of other forms in 

 the course of these Contributions. 



The framework of the basal mass is especially close meshed, 

 on account of an excessively abundant development of synapticular 

 formations, in the bounding surface which is in direct contact 



