178 Scientific Proceedings, Royal Dublin Society. 



Sub-order 2. Trianina. 



Family 1. TETILLIDiE. — Flesh spicules are arculi or spirulse ; 

 the triana are characteristic ; the canal system in the lowest 

 forms is eurypylous, in the highest, aphodal ; the ectosome in the 

 lower forms is the outer epithelium and a thin layer of collenchyme ; 

 in the higher, a highly differentiated cortex ; choanosome, a collen- 

 chymatous mesoderm in the lower forms, sarcenchymatous in the 

 higher. 



Family 2. THENEIDiE. — The flesh spicule is a spini-spirula ; 

 stellates are absent ; the canal system is eurypylous ; the ectosome 

 is not differentiated to form a cortex ; the mesoderm is collen- 

 ehymatous. 



Family 3. STELLETTID^l.— The characteristic flesh spicule is 

 a stellate ; other forms may also be present ; the canal system is 

 aphodal, but approaches the eurypylous type in the lower forms ; 

 the ectosome may, or may not, form a cortex ; the mesoderm of the 

 choanosome a sarcenchyme. 



Family 4. GEODINIDJE. — The characteristic spicule is the 

 globate ; the canal system always aphodal ; the cortex always well 

 differentiated ; the mesoderm of the choanosome a sarcenchyme. 



Sub- order 1. 

 Family 1. PLAKINHXE, Schultze. 



Genus 1. Epallax, g. n. — Plakinidse, with large acerate spicules 

 and small quadriradiate spicules. 



Epallax callocyathus, sp. n. — Sponge, vasiform, expanding 

 towards the upper margin, which is rounded, and gently undulat- 

 ing, produced into a short, strong slender stalk below, by which 

 it is attached ; walls thin ; oscules small, opening into the interior 

 of the cup in longitudinal linear series irregularly alternating ; 

 pores, in sieves on the outer surface, overlying the incurrent canals, 

 which interdigitate with the excurrent canals, both being wide- 

 branching sinuses produced by a folding of the choanosome. Both 

 surfaces hispid ; ectosome thin, collenchymatous ; choanosome, a 

 collenchymatous mesoderm ; eurypylous flagellated chambers. 

 Spicules— (1) acerate, 3-04 by 0-078 mm. ; (2) acerate, 3"93 by 



