104 ART. 1. 1. IJIMA : HEXACTINELLTDA, TIT. 



roughen tlie surftice for the outer | or f of their leugth. They 

 are 75-100 !>■ long, the proximal ray being generally somewhat 

 shorter than the paratangentials in the same spicule. Sections 

 through the wall show that, where the dermalia are superposed 

 upon the hypodermalia, the paratangentials of both are not in 

 direct contact, but there intervenes a space which is nearly as 

 wide as the length of the dermal proximal rays (see fig. 22). 



The gastrcdia (figs. 7 and 8) are likewise hexactinic pinnies. 

 As compared with the dermalia in t'i3 same specimen, they show 

 a general agreement in shape and arrangement but are distinguished 

 by an appreciably weaker development of all the rays. This 

 concerns not so much the length as the thickness of these. The 

 pinular ray, besides being thinner, has spines somewdiat smaller 

 in size and less in number. It does not exceed 33 /-« in the 

 broadest part. 



The above gastral pinnies are replaced on the wall of 

 excurrent canals l)y a less differentiated kind of hexactins, the 

 oxyhexactinic eanalaria (fig. 9). These j)resent about the same 

 axial length as, or are somewhat larger than, the gastralia ; but 

 the rays are very much thinner. All the six rays are alike in 

 appearance ; generally straight but sometimes bent ; and sparsely 

 beset with conical microtubercles on the outer half or less of 

 their length. The transition of the gastralia into the eanalaria 

 at the edge of excurrent apertures is rather abrupt ; nevertheless, 

 there are not totally wanting in this position certain intermediate 

 forms — such as have a pinular ray in an incipient dfgree of 

 differentiation — which may be considered as connecting links 

 between the two. On the other hand, as before mentioned, the 



