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



The scales of the calyx have a convex upper edge which is slightly toothed, usually 

 a middle tooth and two lateral teeth are especially developed, more particularly in the 

 uppermost rows. There are five transverse rows of scales present, of which one is 

 ventral. The ventral scales are slightly different from the dorsal ones in size ; their 

 lateral edges are covered by the lateral scales ; the lower one always covers with its upper 

 edo-e the base of the next above it, so that the scales can slide over one another when 

 the calyx is bent ventrally. 



The opercular scales are short, spear-shaped, with the dorsal and ventral symmetrical, 

 the lateral unequal sided, all grooved in the middle line with expanded base, the lower 

 edge of which is finely toothed. They form, when laid together, a short, obtuse cone. 



Scales of the calyx with rough, radially arranged spines, convex upper surface, 

 which is toothed ; nucleus central with regard to the arc of the upper edge. Length to 

 breadth— 0-2-0 -25 ; 0-15-0-2 ; 0-23-0-27 ; 0-23-0-26 mm. 



Opercular scales ; base of the triangle to height — 0-3-0-12 ; 0-32-0-2 ; 0-38-0-2 mm. 



Scales of the ccenenchyma ; upper layer, nucleus excentric. Length to breadth — 

 0-36-0-15; 0-2-0-17; 0-23-0-27 ; 0-2-0-2 mm.; lower layer— O'l-O-l ; 0-12-0-1 mm. 



Habitat. — Station 171, off the Kermadec Islands; depth, 600 fathoms; bottom, 

 hard gfround. 



2. Thouarella hilgendorfi (Studer) (PI. XXI. fig. 4). 



Pluinarella hihjendorfi, Studer, Monatsber. A. k. preuss. Akad. d. Wiss. Berlin, 1878, p. 618, 

 Taf. ii. fig. 15. 



According to the mode of development of the lateral twigs and the form of the calyx 

 scales, this species may be l^est placed in the genus TliouareUa. This is especially 

 evident from the Challenger specimens, in which the stem is less branched than is the 

 case in the Japanese specimens. In one specimen the stem rises from a flat, expanded, 

 basal, calcareous lamella. Already at a distance of 2 mm. above its root it forks into two 

 equal branches, which rise up parallel with one another to the same height and bear 

 the lateral twigs, without themselves further bifurcating. In a second colony the main 

 stem gives ofi" from either side lateral branches, which both lie in one plane. 



The stem is horny, calcareous, rigid, in all cases oval in transverse section, so that the 

 longer axis is parallel to the direction of the lateral branches. The larger transverse 

 section of the stem near the base reaches 2 to 3 mm. in diameter. The axis is hard, 

 brittle, brown in .spirit, in dried specimens more yellowish ; the surface has a slight golden 

 glitter. Parallel furrows traverse it longitudinally. The twigs are thin, flexible, at the. 

 beginning only 0'5 mm. thick. They arise from three sides of the stem at different 

 heights, and stand off from the stem at nearly right angles. Their points of origin are 

 very close to one another, so that, when superficially examined, they appear to form 



