12 Mr. W. J. Sollas on Stauronema, a new 



is distributed a skeletal network similar to that of the oscular 

 plate. The central sexradiate canal, which is the fundamental 

 part of the skeleton, is of the same size and regularity in both ; 

 and in one specimen the sexradiate nodes are disposed with a 

 regularity so great as to bring about a general arrangement of 

 the fibres into more or less longitudinal, concentric, and radia- 

 ting series. But this arrangement, owing to the want of regu- 

 larity in the course of the canals, is more frequently disturbed 

 by adaptation ; the sexradiate spicules are often turned at 

 various angles from what would be their normal position ; and 

 of course the fibre follows them, with the result that the 

 arrangement of which we spoke is often nothing more than a 

 tendency to an arrangement ; while in most specimens even 

 this amount of regularity would be hard to trace, the sexradiate 

 character of the network almost vanishing or only to be de- 

 tected in the infallible sexradiate canals. 



Superficial Beticulation. — On examining the front face of 

 the anterior plate, there may be seen, in favourable sections, a 

 layer of finer but less regular network proceeding from the 

 outermost meshes of the general skeleton, which lie imme- 

 diately beneath ; and, again, outside this secondary rete, as we 

 may term the finer network, a very thin layer of structure 

 may be sometimes observed, so minute and confused that in 

 section nothing intelligible can be made of it, and for its suc- 

 cessful examination one must have recourse to the method of 

 etching with acid. 



When the face of the attached oscular plate is examined by 

 reflected light in its natural state, it presents a plain surface, 

 the smoothness of which is only disturbed by a faint tubercular 

 appearance ; but on dissolving away its calcitic matrix with 

 nitric acid, a beautiful siliceous network is exposed, which 

 may be best examined under a power of about 100 or 150 

 diameters, and by reflected light. One may see then, in places 

 where the network has wholly broken down, the coarse skele- 

 ton-fibres with their nodes forming a layer immediately 

 beneath, and in this position very commonly furnished with 

 short, erect, conical spines (PI. III. fig. 3) ; above this follows 

 a layer of similar network, but much smaller in mesh, a little 

 less regular, also spined but more abundantly (PI. III. fig. 3, 

 PI. IV. figs. 1,3): four arms of the sexradiate nodes of this 

 network, which we have observed in section as the secondary 

 rete, lie parallel to the surface in square meshes ; of the other 

 two, one passes inwards and joins the general skeleton, and 

 the other projects outwards, normal to the surface, like the 

 " fir-cones " in Farrea occa. These free projecting arms all 

 Bnd at about the same level in cylindrical rounded spinose 



