452 MR. 1'. H. CAUPENTEU ON THE GENUS ACTINOMETBA. 



tain far more of an embryonic character than is usually the case 

 in Antedon ; but the author has met with specimens oiAnt. rosacea 

 in which the metamorphosis is far less complete than usual, and 

 which present in this respect an approximation to Actinometra. 

 A normal rosette of Antedoti rosacea consists of a disk perforated 

 in the centre, with ten rays proceeding from it. Five of these rays 

 are short, triangular in form, and nearly flat ; and their position 

 is interradial, as they are directed to the sutures between the five 

 radials, their apices joining the contiguous pairs of these just 

 between the two adjacent apertures of the central canals. Alter- 

 nating with these five interradial processes of the rosette are five 

 radial spout-like processes, each of which has parallel margins in- 

 flected on its ventral aspect in such a manner as to form a groove, 

 while the process itself is so curved towards its dorsal aspect that 

 this groove reaches the periphery of the rosette and then termi- 

 nates abruptly as if truncated. 



The inflected margins of each of these five radial processes of 

 the rosette are applied to the similarly inflected margins of the 

 dorsal half of an axial furrow lying between the two apertures of 

 the central canal on the internal face of each first radial, so that 

 the two grooves are united into a complete canal. Each of the 

 five canals thus formed contains a diverticulum of the body-cavity; 

 and they terminate blindly in shallow depressions upon the ven- 

 tral surface of the centrodorsal piece on which the first radials 

 rest. 



The rosette is essentially formed out of a secondary calcareous 

 reticulation formed upon the ventral surface of the original basals. 

 The primary or dorsal layer originally constituting them becomes 

 almost entirely absorbed, the ends of the spout-like processes being 

 all that remains of them in the adult Comatula ; for the salient 

 angle of each basal plate which is received between two first radials 

 and the greater part of the centre of its dorsal surface is usually 

 entirely removed. 



Sometimes, however, the removal of the prim ary or dorsal layer 

 at the salient angle of one or more of the five embryonic basals 

 may be incomplete, so that the ends of the curved rays of the 

 rosette exhibit lateral procesf-es which are the remains of the 

 upper margins of tlio primitive basal plates on which the first 

 radials rested. Occasionally the apex of the original basal is left 

 unabsorbed, so that the two lateral curved processes which 

 persist after the removal of the primary external layer along the 



