248 AET. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



mm. Thickness of mys, not more than 65/^- at base. The 

 shaft may in length exceed the paratangential in the same spicule 

 by about half the length of the latter ; in other cases it is only 

 about as long or even somewhat shorter. Compared with the 

 same spicules of certain other species [e.f/., R. capillatus) in which 

 they form a persistent veil, the shaft rays in the present species 

 fall behind considerably in length, a fact which may have bearing 

 on their tendency to ])e readily cast off. 



The dermalia (PI. XVIII., figs. 8-Ll) are j^redominantly 

 rough stauractins. The center of these is generally plain but 

 occasionally shows a gentle swelling on either the external or the 

 internal side or on both sides. Rarely the dei-malia are pentactins 

 in which the unpaired ray is directed proximad while the distal 

 ray is represented by a vestige in the form of a mere swelling. 

 I have found the pentactinic forms especially along the hypoder- 

 raal beams. Still more rarely are the dermalia diactins and 

 tauactins, lying with all their rays in the dermal plane. In the 

 former the suppressed rays are indicated by four knobs around 

 the center ; in the latter the atrophied para tangential usually 

 leaves a knob-like relic, while the ladial rays may or may not 

 be similarly represented. Length of dermalia rays, 114-194/^ 

 (on an average 156/^). Their thickness at base, 9*-12e /^ (on an 

 average 10/^). Sides of the quadrate dermal meshes, on an 

 average 180 /^ 



The grtstralia (PI. XVIII. , fig. 18) are rough hexactins in 

 which the free proximal ray is not specially characterized. Length 

 of rays, 150-230/^ (on an average 180/^) ; breadth at base, 11- 

 15 /^ (on an average 12è /^). Sides of the quadrate gastral meshes 



