28 C. F. JENKIN. 



The body walls are formed of the long branching flagellated chambers 

 (see Fig. 89), which are roughly oval at their proximal ends and are packed 

 closely together on the gastral cortex ; each chamber opens directly into the gastral 

 cavity through an irregular apopyle. Following the flagellated chambers outwards 

 by means of serial tangential sections (Figs. 83 to 87 and 92-97), it will be seen that 

 the chambers usually divide into two branches close above the gastral layer, and that 

 these branches often divide a second time near their distal ends. At the same time it 

 will be seen that the irregular arrangement of the flagellated chambers on the gastral 

 layer gradually changes till at the outer surface it assumes the regular linked pattern 

 which is typical of the genus. 



The Skeleton. — The gastral skeleton consists almost entirely of large tri- and 

 quadriradiates irregularly arranged, with the basal ray pointing more or less down- 

 wards (see Fig. 91). In addition to these there are the paired rays of the chiactines 

 which occur occasionally round the apopyles. 



The gastral skeleton continues into the oscular collar and is modified near the 

 oscular rim, as shown in Fig. 88. The junction of the oscular collar and 

 body wall is shown in Fig. 82, in which the gradual growth of the flagellated 

 chambers may be seen. Near the rim the triradiates almost or entirely disappear, 

 and the quadriradiates are much smaller. There is a fringe of hair oxea (these are 

 absent in one specimen) amongst which are a few stout oxea, apparently of the same 

 sort as those on the distal ends of the flagellated chambers. There are a few thin 

 bent oxea scattered irregularly near the edge. 



The skeleton of the flagellated chambers is of the ordinary articulated type, 

 consisting of small triradiates, which converge at the top of the chamber to form a 

 point which is strengthened by a bundle of oxea of two types which project freely. 

 Every here and there in the proximal joint a chiactine may be found replacing one 

 of the ordinary triradiates; its apical ray projects diagonally into the gastral cavity 

 and across the apopyle. It is the presence of these chiactines which has made it 

 necessary to form the genus Hypodictyon for this species instead of putting it in the 

 genus Tenthrenodes. 



Spicules (Fig. 90). 



Oxea. — There are two sorts of oxea ; — 



(a) Projecting oxea from the distal cones, slightly irregularly bent, some 

 slightly hastate, from 100 m long x 12At thick to 900 y« long x 26iU thick. 

 (6) Hair oxea projecting with [a). 



Triradiates. — There are two forms of triradiates : — 



(c) Large alate triradiates from the gastral layer. Basal ray straight, tapering 

 uniformly to a sharp point, maximum size, 800 m x 10 m- Paired rays, 

 nearly straight, of uniform thickness all along, bluntly pointed, usually 



