168 



sp. a (PI. XXIV, Fig. 3) the vibratile band is seen to pass directly across 

 the body, below the developing Ophiurid, so as to continue directly from 

 one posterolateral arm to the other. A distinct anterior band is represented 

 by the former preoral band of the larva, and moreover in this specimen 

 distinct traces of other vibratile bands are seen, the accordance with the 

 pupa-stage of the Holothurians being thus still more emphasized. There 

 can then be no doubt, that we have really in these Ophiurid larvae a true 

 pupa-stage. — Also in the metamorphosis-stage of 0. formosus there are 



Fig. 93. Ophiopluteus pusillus, species c. A. body skeleton ; B. outer part of postoral rod. ««>/i. 



very slight indications of small parts of vibratile bands in the median part 

 of the body. Most probably they will prove to exist in all forms having 

 a distinct pupa-stage. 



This species was found in the Gulf of Panama, at the island of Taboga, 

 in December 1915; 12 specimens. 



Species c. (PI. XXIX, Fig. 4). The present species differs markedly 

 from the two preceding species in the character of the posterolateral rods, 

 which are provided with long thorns along the inner side, but entirely 

 smooth on the outer side. The body skeleton (Fig. 93, A) forms a pair of 

 rather small, oval meshes, and there is a long often somewhat thorny pro- 

 cess from the recurrent rod; this process is directed ventrally or dorsally, 

 and it is therefore generally broken in the preparations, as also seen in 

 the figure. This thorn may, however, sometimes be lacking. The end rods 

 are rather long, gracefully curved, with a small side branch at some 



