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



6. Spongasteriscus quadricornis, Haeckel. 



Spongasteriscus quadricornis, Haeckel, 1862, Monogr. d. Eadiol., p. 474, Taf. xxviii. figs.. 8-10. 

 Spongodiseus quadricornis, Haeckel, 1860, Monatsber. d. k. prouss. Akad. d. Wiss. Berlin, 

 p. 844. 



Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs ; 

 their form equilateral triangular ; their length smaller than the radius of the large circular central 

 disk, which exhibits in the interior eight to sixteen concentric rings. 



Dimensions. Eadius of the arms 0'2, of the central disk 013 ; basal breadth of the arms 0'08. 



Habitat. Mediterranean (Messina), Haeckel, surface. 



7. Spongasteriscus tetraceros, Haeckel. 



Spongasteriscus tetraceros, Haeckel, 1862, Monogr. d. Eadiol., p. 475. 



Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs ; 

 their form isosceles triangular ; their length larger than the radius of the large elliptical central 

 disk, which exhibits in the interior six to twelve concentric rings. 



Dimensions. Eadius of the arms 016, of the central disk 01 ; basal breadth of the arms 0'06. 



Habitat. Mediterranean (Messina), North Atlantic (Canary Islands), surface. 



8. Spongasteriscus myelastrum, n. sp. 



Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs ; 

 the arms of one pair broader and shorter than the arms of the other pair. Each arm in its basal 

 half simple, in the distal half forked ; ends of the fork branches blunt. In the central disk no 

 concentric rings. (Similar to Myelastrum octocorne, PI. 47, fig. 12, but quite spongy.) 



Dimensions. Eadius of the arms 0'2, basal breadth 0'05, distal breadth 0'02. 



Habitat. North Pacific, Station 236, surface. 



Genus 265. Spongaster, 1 Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. 



Wiss. Berlin, p. 833. 



Definition. S pongodiscida with four spongy arms on the margin of the 

 circular or quadrangular disk, connected by a spongy patagium of different texture. 



The genus Spongaster differs from the foregoing Spongasteriscus in the patagium 

 connecting the spongy arms, and bears therefore to it the same relation as, in the 

 Porodiscida, Histiastrum does to Stauralastrum, or, in the Coccodiscida, Stauractura 

 does to Astractura. The typical specimen, figured by Ehrenberg (Spongaster tetras), 

 exhibits a regular, square disk, as also some other species. In a certain number of other 

 species (formerly united by me with Spongocyclia) the quadrangular disk is bilateral. 



1 Spongaster= Spongy star ; airey/a;, aaTqi>. 



