74 ART. 1. — I. IJIMA : HEXACTINELLTDA, III. 



The äermalia are oxypentactins, which differ but little from 

 parenchymal oxyhexctins except in having one ray less. All the 

 rays are straight or nearly so. The cruciate paratangential rays 

 are in most cases è-lè mm. long as measured from the center ; 

 the unpaired proximal ray is often twice as long as the paratan- 

 gential in the same spicule, and sometimes even longer. Uniformity 

 of size can not therefore be attributed to the dermalia. Not 

 infrequently we meet with exceptionally small and fine-rayed 

 dermalia, which likely are still in an incomplete state of develop- 

 ment. Now, what seems to constitute a characteristic feature of 

 the species is the fact tliat the paratangentials in certain dermalia — 

 not in all — are peculiarly spined (PI. VI., fig. 2). The slender 

 and sharply pointed spines, sometimes small but sometimes 90/^ 

 long, are situated in a row on the outer side of paratangentials, 

 at wide but indefinite intervals (of 34-150/^). As seen in lateral 

 views of paratangentials, the spines mostly start out nearly erect 

 at base but are usually gently curved one way or the other. They 

 never occur numerously, their number on a single ray being not 

 more than six ; often there are only one or two to a ray. Dermalia 

 thus spined are common among the medium-sized elements of the 

 layer. The largest dermalia are, like the smallest, unspined. The 

 paratangentials with spines are seen to run sometimes over, and 

 sometimes under, those without spines. In fact, it seems there exists 

 no rule as to the relative position in layers of the spiny and the 

 smooth dermalia of various sizes. The thin dermal latticework 

 formed by the intersecting of paratangentials at various angles is 

 irregularly meshed. (In the upper part of fig. 8, PI. VI., the 

 dermal latticework is represented, not in section, but as seen 

 obliquely en face). 



