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



The polyps are club-shaped, 2 mm. long, they arise from four sides of the twig, and 

 form too-ether a short ascending spiral. These spirals, however, are not quite regular, 

 sometimes only three polyps form the spiral, in other cases the spiral runs twice round 

 the stem before the origin of one polyp comes into the same line again with the first. 

 Growth takes place at the end of the branches and twigs in a manner quite analogous to 

 that in Thouarella. The scales of the calyx are covered with rough prominences, which 

 often run out into little spines. Those of the uppermost row are broad, with a toothed, 

 convex, upper edge. In the middle line of the scale a keel runs out from the nucleus 

 which is produced into a long pointed or toothed spine, the rough prominences are arranged 

 radially from the nucleus to the edge, and sometimes become merged together into ribs 

 and end in short si^ines. Length to breadth in mm.— 0-37-0 "S ; OS 7-0 -33 ; 0-3-0 -2 ; 

 0-3-0-25. The next lower calyx scales are broader than high, a median rib, running out 

 from the nucleus, is present, but the keel scarcely projects ; on the other hand, lateral 

 spines are well developed. Height to breadth in mm. — 0-15-0-3; 0-26-0-38 ; 0-24- 

 0-37 ; 0-2-0-23. Towards the base of the calyx the spines on the scales disappear. The 

 ventral scales of the calyx are thin, cycloid, without prominent sculpture. The opercular 

 scales are very like those of Thouarella; triangular, with a median longitudinal 

 furrow, which produces a convex keel on the inner side of the calyx scale. The 

 prominences on these scales also are developed up to the point, and the edges are toothed 

 and 23rovided with prominent spines. Height to breadth in mm. — 0-46-0-25; 0-3-0-2; 

 0-33-0-2 ; the latter ventral. 



The scales of the ccenenchyma form a superficial layer of irregular, polygonal, or 

 triangular plates, with marginal nucleus and toothed edges. The rough prominences 

 often run out into sharp, short spines. Length to breadth in mm. — 0-27-0-2 ; 0-18-0-3 ; 

 0-2-0-15; 0-2-0-17; 0-2-0-12. The deeper layer consists of small, generally cycloid, 

 thin little plates with a more central nucleus and weaker sculpture, 0-1-0-08 ; 0-1-0-07 ; 

 0-1-0-1 mm. 



A smaller colony of this species from the same locality, 150 mm. in height, shows some 

 deviations from the form described. The main stem gives off near its base two main 

 branches, which come up to the main stem in strength, expansion and ramification. Their 

 twigs, however, do not come off in the same plane as those of the main stem, but in a 

 plane perpendicular to that. This is caused by the fact that the flat main stem, and the 

 branches, are bent in a spiral ; by adjustment of the spiral the branches and twigs of 

 the main stem and of the branches fall into one plane, which is identical with that of 

 the larger diameter of the stem. The calyces in this form are somewhat smaller than 

 in the foregoino-, 1-5 mm.; still, according to the form and condition of the scales there 

 is no necessity for specific separation. 



Habitat. — Station 135a, off" Inaccessible Island, Tristan da Cunha; depth, 75 fathoms; 

 bottom, hard ground, shells, gravel. 



Station 135c, off Nightingale Island; depth, 100 to 150 fathoms. 



