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



whether this species belongs to the Porodiscida (Amphymenium) or to the Spongodiscida (Spongo- 

 Irachium) or perhaps to the Spongurida (Sponyocore). 



Dimensions. Eadius of each ami 01, greatest breadth 0'03 ; transverse breadth of the 

 patagium 0'05. 



Habitat. North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg. 



3. Amphymenium zygartus, n. sp. (PI. 44, fig. 7). 



Both arms equal, four times as long as broad, with seven to eight joints, slowly decreasing in size 

 towards the blunt end. Patagium incomplete, protecting only the middle part of the shell on 

 both sides ; on each side two parallel lattice-plates, connected by transverse radial beams, 

 perpendicular to the surface. Perimeter nearly rectilinear. (Resembles much certain forms of 

 Zygartus, PL 40, but is a true Discoid, no Prunoid.) Compare also PI. 45, fig. 8. 



Dimensions. Piadius of each arm 0'2, greatest breadth O'Oo ; transverse breadth of the 

 patagium Oil. 



Habitat. Pacific, central area, Station 271, surface. 



4. Amphymenium monstrosum, n. sp. (PI. 44, fig. 11). 



Both arms equal, little longer than broad, with six to seven convex joints. The axis of both 

 arms is riot common and straight, as in all other species of this genus, but broken, therefore the 

 incomplete patagium, which envelops only two to three joints of the arms, is on one side convex, on 

 the other side concave; it is formed by a simple lattice-plate, connected with the arms by numerous 

 radial beams. This anomalous form, seen only once, may perhaps be a monstrosity of Euchitonia. 



'Dimensions. Eadius of each arm 012, greatest breadth 0'06 ; transverse breadth of the 

 patagium O'l 3. 



Habitat. South Pacific, Station 290, surface. 



Subgenus 2. Ommathymcnium, Haeckel. 



Definition. Both opposite arms of the same size and form, armed at the distal end 

 witli terminal spines. 



5. Amphymenium amphistylium, n. sp. (PI. 44, fig. 9). 



Both arms equal, three tunes as long as broad, thickened towards the truncated distal end, and 

 armed with a strong pyramidal terminal spine. Each arm with seven joints, separated by convex, 

 transverse septa, and halved by a radial beam lying in the longitudinal axis. Patagium incomplete, 

 cylindrical, enveloping only the middle part of the shell. 



Dimensions. Radius of each arm 018, greatest breadth O'OG ; transverse breadth of the 

 patagium - 08. 



Habitat. North Atlantic, Station 354, surface. 



