82 



wltile to olTor this sui^gestion as to the true nature of the rather mysterious 

 Auricularia i)uraduxa. For the delhiite solution of the problem direct 

 observations of the living larvae or, at least, considerably more material 

 than at present available will be necessary. 



Species b. A single specimen of this species, which is, evidently, 

 closelv related to species a, was found in a plankton sample from the 

 Ciulf of Panama, at Taboga, (January 1916). It is in a poor state of pre- 



Fig. 31. Skeleton of Echinopluteiis transversus, species b. A. From the ventral. B. from 

 the dorsal side. "7i- Letters as in fig. 30. 



servation so that only the skeleton can be figured and described; but 

 there'^is no reason to expect that it would show noteworthy diflerences 

 from the species a in regard to the general shape of the larval body. Ap- 

 parently it difTers markedly in shape from species a, the postoral arms 

 being nearly erect; this, however, evidently is due only to muscular con- 

 traction (comp. species c, PI. XIII, Fig. I). 



The skeleton (Fig. 31), although in its main features like that of species 

 a, shows some very characteristic diflerences from that species. The 

 ventral transverse rods form an arch as in that species, but are not so 

 high and somewhat more widened and thorny at the end. The ventral 

 recurrent rods are especially characteristic, being hookshaped, not bifur- 

 cating at the point, with one or two small thorns along the sides. They 



