81 



transverse rods are directed nearly straight upwards, bending inwards 

 at the point, so that they meet and together form an elegant arch; thev 

 are slightly widened and serraied at the poinl. From their base issues a 

 backward prolongation, a 'ventral recurrent rod", which soon bifurcates, 

 each sending one branch, llie "supplementary transverse rod", upwards, 

 where they join over the middle of the stomach, the other branch going 

 straight downwards, crossing the body rod. Both these branches are 

 simple rods in this species, while in the other species the}' undergo a re- 

 markable specialisation, species b being, however, peculiar in this regard. 

 The antero-lateral rods are well developed, simple, with few small thorns 

 irregularly disposed. The recurrent rod is well developed, smooth, 

 slightly longer than the body rod; from about its middle a short, simple, 

 somewhat widened transverse rod proceeds recalling the transverse rod 

 of an OphiopluU'us, with which it is, hovewer, not to be compared, of 

 course; it is iiomologous with the connecting rod of Echinoid larvae with 

 a typical basket structure, as e. g. the larvae of Astropyga or Tripneiistes. 

 At the base of the postoral rod, close outside the point of issue of the 

 antero-lateral rod, a rather long, simple thorn is found. The postero-dorsal 

 rod, the posterior transverse rod and the dorsal arch have not yet appeared. 



There is some probability that the 'Auriciilaria paradoxa' (from 

 0°4' N, 46°6' W) which 1 described in the "Echinodermenlarven der 

 Plankton-Expedition" (p. 21 Taf. 1, Fig. 7) really is a decalcified specimen 

 of this species. It may seem strange that an Echinoid-larva should have 

 been mistaken for an Auricularia; but a glance at the figure will show 

 that there is really nothing which could indicate that it might be an 

 Echinoid-larva. the shape being just as unusual for an Echinoplutens as 

 it is for an Auricularia; as long as the Echinoplulcus Iransversus was un- 

 known, liardly anybody could have fancied that this might be an Echi- 

 noid-larva. Now it is easy to see that a form like Echinoplutens Iransversus, 

 species a, when decalcified and otherwise not too well preserved — as 

 was the case with that larva would get very much the same ajipearance 

 as the "Auricularia paradoxa". The compUcated folds of the vibratile 

 band, of course, do not very well suit the rather simple course of the 

 band in the single specimen of the present species of Echinoplutens Irans- 

 versus; as, however, this is a younger stage, it is quite conceivable that 

 the band may be more developed in the older stages of this larva. — 

 The species c would hardly come into consideration, the band being 

 simple there also in a further advanced stage, so that it could certainly 

 not give rise to the complicated folds of "Auricularia paradoxa" when 

 decalcified; the postoral arms of this species are also much longer. 



Although still sonu'what problematical I have deemed it well worth 



11 



