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



In the calyces these spiny scales are arranged transversely around the periphery, and 

 form new areas of spiny scales, each scale with concave deeply-toothed lower edge and 

 convex upper edge, over which spines project. These scales are bent on the surface so 

 as to correspond to the curvature of the body wall. Height to breadth in mm. — 0"05-0"18 ; 

 0-07-0-14; 0-07-0-1. 



The scales of the tentacles are similarly formed, and spiny. 



Colour in spirit, yellowish -white. 



This species was first described by Lamarck, and has been very well figured by 

 Lamouroux. 



Habitat. — Station 162, off" East Moncceur Island, Bass Strait ; depth, 38 fathoms ; 

 bottom, sand and shells. Three specimens. 



The specimen in the Jardin des Plantes in Paris was collected by Peron and Lesueur 

 from Australia. 



During the voyage of the " Gazelle " one example was obtained ofi" the north-west 

 coast of Australia from a depth of 50 fathoms. 



Genus 3. Acanthoisis, n. gen. 



Colony branched, the ramification takes place in one plane, plume-like. The 

 ccenenchyma is relatively thick and allows the jointed axis to show through only at the 

 beginning of the stem. The polyps are arranged in close spirals on the stem and 

 branches. They are cylindrical and upright, arising with broad bases, evenly truncated 

 at the end. The tentacles are short, not retractile; in repose they bend together inwards 

 over the opening of the calyx from their origin, so that they lie horizontally over the 

 opening of the calyx and close it. The points are then bent inwards and the pinnules 

 folded in, forming an eight-rayed star. 



The axis consists of horny and calcareous joints, of which the calcareous joints in the 

 stem are about twice as long as the horny ones. The branches on both sides arise from the 

 calcareous joints, but sometimes so high up that the first horny joint of the branch at 

 the same time touches the horny joint of the stem. This relation, however, only occurs 

 in the older, thicker branches. The calcareous joints exhibit deep longitudinal furrows, 

 which are separated from one another by sharp longitudinal ribs. The edge of each rib 

 is split into sharp teeth, which stand upright in the middle of the joint, but at the two 

 ends are bent towards these. The deep furrows between the ribs are partially filled, 

 with warty, spindle-shaped spicules, which accompany the longitudinal canals. The 

 overlying ccBnenchyma contains longitudinally placed, flat, longish calcareous bodies with 

 strongly toothed edges, unsymmetrically shaped ; in the polyps these calcareous bodies 

 become larger and broader, and are deposited peripherally in the body wall with the 

 toothed edges interlocking. In the tentacles similarly formed calcareous bodies are 



