152 



of the posterolateral arms are continuing across the body, below the devel- 

 oping Ophiurid. At the anterior end there is another transverse band, ap- 

 parently derived directly from the preoral band. Thus a remarkable rear- 

 rangement of the vibratile bands takes place in this form, something corre- 

 sponding to what takes place in the transformation of the Auricularia into 

 the pupa-stage (Cf. p. 125). A similar case was observed in Ophiopluteus 

 pusillus, species b (PI. XXIX, Fig. 3) and 0. imdiilatus, species a (PI. XXIV, 

 Fig. 3). 



Species b. (PI. XXVII, Fig. 2). This species differs so conspicuously 

 from species a as regards its shape that it may seem doubtful, whether it 



Fig. 80. Skeleton of Ophiopluleux /ormosus, species b. 29 %. 



really belongs to the same type. The inner arms are one and a half to two 

 times, the posterolateral ones more than four times the body length. The 

 arms are narrow, rounded, not broad and flattened as in species a. On 

 the other hand the skeleton (Fig. 80) so closely resembles that of species 

 a that only very small differences can be pointed out, the main thing 

 being that the transverse rods are somewhat more robust, the indentations 

 at the ends being less deep. Perhaps the shape of the meshes of the body 

 skeleton will prove a little different. In species a the meshes are somewhat 

 narrower at the lower end, which does not appear to be the case in the 

 present species; but as there is only one specimen, and that one even 

 showing a slight difference in the shape of the two sides of the body skele- 

 ton, this feature is not to be relied upon as a specific difference. The thorns 

 on the posterolateral rods are blunt and more distant than in species a. 

 (Fig. 82, B). 



One single specimen, fairly well preserved, from the Red Sea, 24 43' N. 

 35 45' E. 10/XI. 1899. 



