22 



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



be clearly seen in a specimen whicli Mr. Carter kindly sent 

 me to illustrate this point. The skeletons of the two, how- 

 ever, are in one respect widely different. In Aphrocallistes 

 the imbedded sexradiates are subject to great variations in the 

 disposition of their rays, five, or even all six, radii being some- 

 times brought into one plane, while two or more of these rays 

 may be and often are enveloped in one and the same fibre ; 

 so that the nodes of the resulting network are as often as not 

 sexrotulate in the same plane, and the intermeshes consequently 

 triangular. In Stauronema, on the contrary, the spicule main- 

 tains a rigid stereometry, never departing from a rectangular 

 triaxial type, and the rete is usually quadrangular ; and though 

 it may vary in this respect, yet when it does so the change is 

 never due to the departure of any radius of the original spicules 

 from strict rectangularity, but results from a different disposi- 

 tion of the entire spicules with regard to one another. This 

 difference is seen in the following diagrams : — 



Fis-. 8. 



Fia-. 9. 



Fig. 8 shows quinqneradiate nodes (q) of Stauronema, due to the rela- 

 tive disposition of the spicules (s). 



Fig. 9 shows the quinque- and sexradiate nodes of ji2JhrocaUistes, and 

 the sexradiate spictiles (s) with rays making various angles with each 

 other. At a two rays of a spicule are seen lying approximately parallel 

 and imbedded in the same fibre. 



In this character Stauronema agrees with Farrea occa, where 

 also we find the same persistency in the form of the skeleton- 

 spicule ; and to this example may be added the exteraal net 

 oi Eubrochus {^oWsl^) and the Ventriculitidse generally. But, 

 as we have said, the Ventriculites are excluded by the presence 

 of the lantern about the nodes ; and Farrea is so of course by 

 the fact that its skeleton consists of but a single layer of 

 lattice-work ; Eubrochus exhibits a more delicate and less 

 regular internal skeleton, and is altogether a very different 

 sponge. 



The place oi Stauronema amongst its relations may perhaps 

 be best illustrated by the following Table, which is a classifi- 



