STUDIES ON THE OOMPARATTVE ANATOMY OF SPONGES. 229 



It might, perhaps, be regarded as a degenerate Heterocoele 

 which has lost its 'radial symmetry, but the facts do not 

 appear to me to warrant this hypothesis. 



Family 2. — Sycettid^, Dendy (4). 



Diagnosis.— Flagellated chambers elongated, arranged 

 radially around a central gastral cavity, their ends projecting 

 more or less on the dermal surface, and not covered over by a 

 continuous dermal cortex. Tubar skeleton articulate. 



Remarks. — This family is equivalent to van Lendenfeld's 

 (10) two sub-families Sycanthinse and Syconinse taken to- 

 gether. As I have already pointed out, his genus Sy cantha 

 is probably but a slight modification of the ordinary Sycon 

 type. The name Sycettid^ is adopted partly because the 

 genus Sycetta is the simplest of the three included in the 

 family, and partly to avoid confusion with the much more 

 comprehensive Syconidse of previous writers, such as Pole- 

 jaeff (8). 



Genus 2.— Sycetta (Haeckel [5], emend.). 



Diagnosis. — Radial chambers separate from one another, 

 and without tufts of oxea on their distal ends. 



Remarks. — This genus, as here maintained, is much less 

 comprehensive than was originally intended by its author (5). 

 Haeckel included in the genus all Syconoid species in which 

 triradiate spicules alone entered into the composition of the 

 skeletons, and thus was obliged to group together such struc- 

 turally different species as S. primitiva and S. stanridia; 

 while he had to exclude S. conifera simply because some of 

 the triradiates develop an apical ray, and thus become 

 quadriradiate. Von Lendenfeld also confined his diagnosis of 

 the genus to the character of the spiculation (10), but modified 

 it so as to include S. conifera. Polejaeff (8) merged the 

 genus into Sycon. If, however, we include in the genus only 

 those species which, like Haeckel's Sycetta primitiva and 

 S. (Sycaltis) conifera, conform in skeletal characters and 

 canal system to the diagnosis given above, we shall have left a 



