404 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 2. Margaritella, 0. Schmidt. 



With the single species Margaritella cceloiotijchioides, 0. Schmidt. 



From the somewhat indistinct description and figure given by 0. Schmidt/ the 

 body of this sponge forms a flat cup, the wall of which consists of a system of connected 

 tubes and equally wide intercanals. The dictyonal framework enclosing polyhedral 

 meshes consists of weakly developed, richly tubercled beams, which are united by slightly 

 thickened nodes of intersection. The latter bear tubercle-like warts where they occur 

 near the surface of the network. The parenchyma contains loose spicules in the form 

 of weakly developed oxyhexacts, delicate oxyhexasters with a few short terminals and 

 very short or wholly reduced principals, and finally somewhat substantial sphgero- 

 hexasters in which the principal rays are often so much shortened and connected by 

 siliceous masses into a central knot, that the numerous long knobbed terminals appear as 

 if radiated out directly from the centre. The dermal skeleton contains rough pentacts in 

 which the four tangential rays are knobbed, while the proximal radial is simply rounded 

 off" or somewhat narrowed at its extremity. Havana, 158 fathoms. 



Genus 3. Scleroplegma, 0. Schmidt. 



Thick-walled cup or cylinder in which " the brittle parietal feltwork consists of 

 round or prismatic tubes, which run for the most part obliquely from the outside inwards, 

 either isolated or united in small numbers, and open into the gastral cavity." Between 

 the tubes there are irregular intercanals.' 



The only species really known to me is Scleroplegma conicum, 0. Schmidt. 



The somewhat smooth internal wall of the spherical goblet exhibits the openings of 

 several wide tubes, arranged in toleral^ly distinct longitudinal rows. The external 

 surface is traversed by a labjrrinth of grooves. The beams of the polyhedral meshwork 

 are beset with transverse rows of conical tubercles, and are united in nodes of inter- 

 section, which are thickened especially on the surface of the lattice-work, and beset 

 with groups of tubercle-like warts on the free surface. The loose spicules are quite 

 undetermined. West Indies, 292 fathoms. 



Genus 4. Myliusia, Gray. 



With the single species, Myliusia callocyathus, Gray. 



A thick-walled substantial cup, with an originally simple plate-shaped wall, from 

 which, by continued parietal folding, a system of tubes has arisen. This system com- 



1 Spongien des Meerbusens von Mexico, p. 54, Taf. vii. fig. 7. 

 - 0. Sclimidt, loc. cit., p. 56. 



