226 AKT. 7. — I. IJIMA : HEXACTINELLIDA, IV. 



paratangential in the same spicule. The pentactins situated near 

 the oscular margin and already externally protruded as prostalia, 

 I have found to be unusually small, measuring not more than 

 half a millimeter in the length of paratangentials, which in these 

 small pentactins are generally arranged in the form of a regular 

 cross to each. 



This cruciate arrangement of the paratangentials also occurs, 

 but only occasionally, in the larger pentactins lower down on the 

 sponge. In by far the greater number of these the rays referred 

 to are paratropal. The paratropism is carried out to varying 

 degrees in different spicules. In some cases, one of the four 

 angles formed by the rays is simj)ly obtuse while the rest are all 

 acute though greater than 30° each ; in other cases the four rays 

 form only three angles, each of about 30° or less. It is to be 

 noted that whenever two or more paratropal pentactins form a close 

 group, whether by themselves alone or in company with diactinic 

 prostalia, the paratangentials of each pentactin are, as it were, 

 pushed away from the center of that group (PL XVI., fig. 14). 

 I shall have to return to this point under Rhabdocalyptus victor. 



All the rays of the pentactins are at first smooth except at 

 the ends which are rough. So are they in most of the spicules 

 in the hypodermal situation ; however, here and there among 

 these are to be seen such as show the paratangential cross finely 

 rough all over. The roughness is caused by minute, erect and 

 sharply pointed processes, which, when seen from above, appear 

 to be somewhat laterally compressed so as to present a shape 

 elongated in the direction of tlie axis of the ray they beset (PL 

 XYL, fig. 13). The microspines reminds me of those I have 

 seen on the prostal pentactins of Scyphidium lo7igispina. To 

 judge from what appear to represent developmental stages, the 



