STUDIES ON THE COMPARATIVE ANATOMY OP SPONGES. 235 



arranged radially around the central gastral cavity. The 

 skeleton consists exclusively of oxeote spicules. 



E/Cmarks. — The only known species of this genus is 

 Haeckel's Sycyssa Huxleyi, from the Adriatic (5). The 

 genus occupies a very isolated position. The remarkable 

 skeletal characters upon which it is based have been discussed 

 on a previous page. 



Genus 10. — Leucandra (Haeckel [5], emend.), figs. 16^ 17. 



Diagnosis. — The flagellated chambers are spherical or sac- 

 shaped, never arranged radially around the central gastral 

 cavity, with which (or with the main exhalant canals derived 

 therefrom) they communicate by a more or less complicated 

 exhalant canal system. The skeleton of the chamber layer is 

 composed of irregularly scattered radiate spicules, but it may 

 still present traces of its derivation from a radially symmetrical 

 type, in the presence of a few subgastral sagittal triradiates. 



Remarks. — This genus, as here maintained, is still a very 

 comprehensive one, and does not correspond exactly to any 

 which have hitherto been proposed. It includes many species 

 which would fall under PolejaeS'^s Leuconia (8), but that 

 author frankly admits that his Leuconia requires sub- 

 dividing; and, moreover, Vosmaer (14) has shown that Bower- 

 bank^s name Leuconia, adopted by Polejaeff, was previously 

 occupied byagenusof MoUusca. I therefore agree with Vosmaer 

 in adopting Haeckel's name Leucandra, but as that genus was 

 based entirely upon the presence of certain forms of spicules, 

 without regard to their arrangement, I cannot accept it in the 

 sense originally intended. On the same principle, I include in 

 the genus Haeckel's species of Leucetta, as I do not believe the 

 mere absence of quadriradiate or oxeote spicules, or both, to 

 be of generic significance. Indeed, I was strongly inclined to 

 adopt the name Leucetta, on grounds of priority, for the 

 genus as now constituted; but considering that Leucandra, 

 as employed by Haeckel and Vosmaer, makes the nearest 

 approach to the genus as now characterised, and considering 

 also that the name Leucetta has been adopted by Polejaeff 



