147 



straight. However, much stress cannot be laid on this character, which 

 may to some extent depend on preservation. It appears that the small 

 extra arms are less developed than in species a. In the specimen figured 

 the ventral ones are distinct, but quite small; the dorsal ones are not 

 distinct. In another specimen one of the dorsal arms is very distinct. That 

 they will be developed, both pairs, in the fully formed larvae ( — the hydro- 

 coel has not begun to form lobes in any of the specimens — ) I have no doubt. 

 The skeleton (Fig. 75). The posterolateral rods are canaliculate almost 

 from the base to near the tip. They are naked along the outer side, ex- 

 cepting one or a very few small prominences so placed off the thorns on 



Fig. 74. Skeleton of Ophiopluteus opulentus, species b. ^'"/i- 



the inner side, that a slight thickening is formed (Fig. 76) ; there is gener- 

 ally such a thickening in the lower part, sometimes also a few farther out, 

 and in that case the rod gets a peculiar, somewhat nodulose appearance. 

 The dorsal extra rods are smaller than the ventral ones. The processes 

 from the transverse rods are well developed; the ends of the transverse 

 rods are distinctly widened. 



Of this species there are three specimens from Christiansted, St. Cruz, 

 West Indies, taken by Mr. H. Faye, 16/VI. 1915. There are also some 

 younger specimens, which may possibly belong to the same species, but 

 the distinguishing characters not yet being fully developed (— the extra 

 rods have not appeared — ) I cannot state definitely whether they do 

 really do so. 



To this species, however, some curious "specimens" (PI. XX, Figs. 3—5) 

 undoubtedly belong, which consist only of the body skeleton and the po- 

 sterolateral arms, these arms still having their vibratile band intact. AH 

 the rest of the larva has disappeared. This is a case analogous to what 

 obtains in the Ophiothrix-larya, viz. that the posterolateral rods are not 



19* 



