93 



Aspidodiadi'inalids into consideration. liut then no other regular Kchin- 

 oids are left, and we are forced to assume the possibihLy that ophicephal- 

 ous pedicellariae of the shape occurring in these larva' may perhaps occur 

 as a sort of embryonal organs, corresponding to the embryonal spines of 

 young regular Echinoids, in young, just metamorphosed urchins, being 

 very soon lost, like the embryonal spines. If that were the case, also Ci- 

 darids, Clypeastroids, Kchinoneids and Spalangoids w^ould come into 

 consideration. Of the Clypeastroids so many dilTerent larvae are known 

 from previous researches or described here, all being of a very uniform 

 typo, tlial il is exceedingly improbable that the Echinopluteus imnsversiis 

 could belong to lii;it family. Of the Echinoneids there are not sufficient 

 forms known to account for the presence of two species of larva^ in the 

 Gulf of Panama closely related to two West-Indian species. If the larvae 

 species a and c were really only one species in different stages of develop- 

 ment, and in the same way species b and d only one species, we would 

 have a species of Rhyncholainpas (Cassidiilus) corresponding to each of 

 them, and then species e and f might be referred to Echinoneus, the West- 

 indian species of which is — according to H. L. Clark — identical with 

 the indopacific Echinonem cycloslomus. This would also account well for 

 the fact that the larva e and f are so similar that they seem hardly disting- 

 uishable. But I fail to see how the species a and c or b and d could possibly 

 be the same species. That would require a so remarkable transformation 

 of the different skeletal parts that it is hardly conceivable. II would not 

 consist in the resorption of some parts and new formation of others, as 

 is the case in so many Echinoid larva on their passing from the first to 

 the second larval stage; but it would be a real and complete transforma- 

 tion of the same skeletal parts, especially the body rod, the ventral and 

 supplementary transverse rod, and even in the course of very short time, 

 the specimen of species c being only in a very slightly more advanced 

 stage of development than that of species a. as is also the case with the 

 specimen of s])ecies d in comparison with that of species b. Tiie idea of 

 the identity of s[)ecies a and c, or of species b and d then evidently must 

 be dropped, and also the suggestion that these "species" miglit represent 

 only individual variations of one species would seem equally absurd. - 

 Against the idea that those larva might belong to Echinoneus and Rluin- 

 chnlampas the fact also speaks that the larva of OlUjopodia {Echinobiissus) 

 rircns is of the type of the Clypeastroid larva* (comp. below), so that il 

 is highly improbable that the closely related Rhynclwlampas should have 

 a larval form so entirely difTerent. 



flial tlio Echinopluteus transversus might belong to some Spatangoid is 

 by no means more probable. All the Spatangoid larva known belong to 



