198 ARTHUR BENDY. 



irregularly arranged bundles of very slender oxea, and (2) a 

 subgastral layer composed of regularly arranged, parallel, 

 longitudinal bundles of large, stout oxea : this is comparable 

 to the similar layer in U tell a. The tubar or chamber skeleton 

 is composed of the inner ends of enormous radially arranged 

 oxeote spicules, comparable to those found in Grantia 

 Vosmaeri, but larger and apparently more regularly arranged. 

 The outer ends of these spicules project far beyond the dermal 

 surface. The skeleton of the dermal cortex is composed of 

 (1) a layer of very slender oxea, arranged irregularly but 

 parallel to the dermal surface, and (2) a layer of very slender 

 oxea, arranged radially and forming a kind of pile over the 

 outer surface, as in so many Heterocoele sponges. 



This genus, of which the only known species is Sycyssa 

 Huxleyi, from the Adriatic, must be regarded as possessing a 

 very aberrant type of skeleton, and occupying a very isolated 

 position in the group. 



Leucandra (figs. 16, 17). 



To understand the structure of the skeleton in this genus 

 VFe must return to that of Grantia, of which it is evidently a 

 modification. We saw how in Grantia Vosmaeri (fig. 10) — 

 where the exhalant canals have begun to elongate and the 

 chambers to shorten, and where the mesoderm is very strongly 

 developed in the inner half of the sponge wall — the skeleton 

 has begun to lose its regular articulate character. The same 

 thing is carried to a much greater extent in Leucandra, 

 where the canal system has lost its symmetry and the 

 skeleton has followed suit (figs. 16, 17). The skeleton of the 

 gastral and dermal cortex, however, retains the same structure 

 as in Grantia; it is only the skeleton of the chamber layer 

 which is affected by the changes in the canal system. Hence 

 we find that in a typical Leucandra (fig. 16) the skeleton of 

 the gastral cortex is made up principally of quadriradiate 

 spicules whose apical rays project into the gastral cavity, 

 while the skeleton of the dermal cortex is made up of tri- 

 radiates, lying parallel to the dermal surface, and longer or 



