147 



straighL However, much stress cannot be laid on this character, which 

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

 extra arms are less developed I ban 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 iully 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 ofi" the thorns on 



Fig. 74. Skeleton of Ophioplnleus opukniiis, species b. "•*/,. 



the inner side, Llial 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. All 

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

 obtains in Ihe Op/i/o/Zi/n-larva, viz. that the posterolateral rods are not 



19* 



