228 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



ever, and having found the same diactins in like abundance over 

 the entire gastral surface of the tlyee specimens examined, I have 

 come to see no inappropriateness in calling them the gastralia. 

 Moreover, a second Acanthascine species with diactinic gastralia 

 is now known, viz., Rhabdocalypius phmiodigiiaius K. Kirk p. It 

 should, however, be said that the gastralia in the present species 

 seem to intergrade with the parench3analia by an uninterrupted 

 series of transitional forms. Like the dermalia, the gastralia lie 

 in quite irregular disposition on the gastral surface (PI. XVI., 

 lig. 16). 



Many of the gastralia are much like the dermalia both in 

 dimensions and general appearance. AVhat may perhaps be men- 

 tioned as slight deviations shown by the former are the facts that 

 the microtubercles on the surface are on the whole more sparse 

 and more thinly scattered and that the middle of the spicules is 

 frequently, but not always, marked by a gentle annular swelling. 

 Many others of the gastral diactins are considerably larger (PI. 

 XVL, fig. 6), ac(i(uiring characters approaching tliose of parenchy- 

 mal diactins. AVith the increase in size, the microtuberculation 

 becomes more and more sparse except at the ends, finally rendering 

 the middle parts of the spicules perfectly smooth. 



In one specimen (No. 226), in wliich I have studied the 

 spiculation most closely, I find the gastral skeleton in the prox- 

 imity of the osculum scarcely at all distinguishable as to its 

 elements from the dermal. That is to say, the gastralia in that 

 region contain, besides an abundance of the rough diactins, 

 occasional stauractinic and tauactinic forms, underlying which 

 spicules are some hypogastral pentactins with cruciate paratan- 

 gentials. Deeper down and in by far the greater part of the 

 gastral surface, the hypogastral pentactins are not found, while 



