Pv. OKixosEANA. — spicrLArroK. 229 



pleciella. Ou the gastral surface there are seen the bundles 

 already referred to, the course of which more closely approaches 

 the transverse than that of any of those visible ou the external 

 side. — Superiorly, the fusion of spicules gradually diminishes in 

 degree and extent ; the interweaving of the fused bundles becomes 

 looser ; finally, each of these runs out into fretted, tuft-like 

 strands. At the same time the hard external ridges disappear, 

 becoming replaced in the living state by the loosely supported 

 ledges, which are of course lost after maceration. 



Spiculation. 



The two specimens shown in PI. YII, tigs. 1 & 2 (8c. Coll. 

 Mus. Nos. 487 & 488), were principally made use of in my 

 study of the spiculation in full-grown individuals. 



The jyrincipalia in the parenchymal bundles are large oxy- 

 diactius, which may attain a length of 35 mm. or more and a 

 breadth of 220 « in the thickest portion. They are nearly 

 straight or gently bent, without an elbow-like bending at the 

 middle. Towards both extremities they attenuate to thin, smooth 

 or rough-surfaced, pointed ends. — The coinilalia, accompanying 

 the above principalia in a copious quantity, are mainly slender 

 diactins, — not thetactins as in Euplectella. They are usually 

 10-lG !>■ thick ; generally smooth but occasionally annulated or 

 tubercled at the spicular center ; subterminally rough-surfaced, 

 the very end being smooth and rounded or conically pointed in 

 the usual wav. Just the same diactins as the comitalia occur in 

 all parts of the wall either in loose arrangement or in strands by 

 themselves. 



