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



Subgenus 2. Amphirrhopella, Haeckel. 

 Definition. Both opposite arms of similar size and form, with terminal spines. 



3. Amphirrhopalum bigeminum, n. sp. 



Both arms equal, in the proximal larger half simple, in the distal smaller half forked ; each 

 branch triangular, with a strong conical terminal spine. Axis of the branches straight. (Resembles 

 Dicranastrum cornutum, PL 45, fig. 2, but without lateral arms.) 



Dimensions. Eadius of the arms (without spines) - 15, basal breadth 0'03 ; breadth of the 

 bifurcation - 08. 



Habitat. South Pacific, Station 284, surface. 



4. Amphirrhopalum echinatum, n. sp. (PL 45, fig. 10). 



Both arms equal, in the proximal smaller half simple, nearly square, in the distal larger half 

 forked ; the branches thorny, armed at the end with numerous spines, one larger on the terminal 

 pole of the concavely curved arm-axis. 



Dimensions. Radius of the arms (without spines) 015, basal breadth O05 ; breadth of 

 branches 0'03. 



Habitat. Pacific, central area, Station 266, depth 2750 fathoms. 



Subgenus 3. Amphirrhopoma, Haeckel. 

 Definition. Both opposite arms of different size or form, without terminal spines. 



5. Amphirrhopalum ypsilon, n. sp. 



Both arms very different. Larger arm simple, egg-shaped, twice as long as broad ; smaller arm in 

 the basal half simple, nearly square, in the distal half forked ; both branches egg-shaped, blunt. 

 (Resembles Amphicraspedum wyvilleanum, PI. 45, fig. 12, but wants the patagiuni.) 



Dimensions. Radius of the larger simple arm 018, breadth 0'09 ; radius of the smaller forked 

 arm 015, breadth of its branches 0'05. 



Habitat. Indian Ocean, Madagascar, Rabbe, surface. 



Genus 226. Amphicraspedum, 1 Haeckel, 1881, Prodromus, p. 460. 



Definition. P orodiscida with two chambered arms, opposite in one axis, 

 connected by a lateral patagium ; one arm or both forked at the distal end. 



The genus Amphicraspedum exhibits the same bifurcation of the arms as does^ 

 Amphirrhopalum, but differs from this ancestral form in the development of a patagium, 

 an external connecticulum between the arms, which envelops the disk totally or partially. 



1 Amphicrispedum -Shell with borders on both sides ; 



