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



The genus Stauracantha differs from its ancestral form, Xiphacantha, in the 

 ramification of the four crossed apophyses on each spine. These bear either lateral 

 branches, which are parallel to the cross axes of the radial spine itself (subgenus 

 Stauracanthonium), or they are forked, with divergent branches not parallel to those 

 cross axes (subgenus Stauracanthidium). Both subgenera may perhaps be better 

 separated as genera. They form the transition to the Stauraspida. 



Subgenus 1. Stauracanthonium, Haeckel. . 



Definition. Apophyses of the radial spines not forked, but crossed by perpendicular 

 branches, which are placed in tangential planes and parallel to the cross axes of the 

 quadrangular spine itself. 



1. Stauracantha orthostaura, n. sp. (PI. 130, fig. 5). 



Spines four-sided prismatic, with simple apex and small leaf-cross at the base ; with four 

 thin slender conical apophyses in the proximal third. Each apophysis represents a regular 

 rectangular cross, being intersected in its middle by one perpendicular rod of its own length. 



Dimensions. Length of the spines 0'3, breadth 0'02 ; distance of the apophyses from the apex 

 015 to 0-2. 



Habitat. South Pacific, Station 169, surface. 



2. Stauracantha tetrastaura, n. sp. 



Spines four-winged prismatic, with four broad prominent edges, pyramidal apex, and large 

 basal leaf-cross, with four broad compressed apophyses a"bout in the middle. Each apophysis 

 represents a vertical lamella (placed in a meridian} with convex distal and concave proximal edge, 

 and is crossed in its apical part by one perpendicular short rod. 



Dimensions. Length of the spines 0'5, breadth 0'03; distance of the apophyses from the 

 centre 0'2. 



Habitat. Central Pacific, Station 272, surface. 



3. Stauracantha diplostaura, n. sp. 



Spines four-sided prismatic, with truncated apex and broad basal leaf-cross ; in the proximal 

 half with four slender conical apophyses. Each apophysis is crossed in its apical half at right 

 angles by two short parallel transverse rods. 



Dimensions. Length of the spines 0'32, breadth 0'012 ; distance of the apophyses from the 

 centre OH. 



Habitat. South Pacific, Station 291, surface. 



