93 



Aspidodiadematids into consideration. But then no other regular Echin- 

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

 ous pedicellariae of the shape occurring in these larvae 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, Echinoneids and Spatangoids would come into 

 consideration. Of the Clypeastroids so many different larvse are known 

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

 type, that it is exceedingly improbable that the Echinopluteus transversus 

 could belong to that family. Of the Echinoneids there are not sufficient 

 forms known to account for the presence of two species of larvse in the 

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

 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 Rhyncholampas {Cassidulus) 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 Echinoneus cyclostomus. This would also account well for 

 the fact that the larvae 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. It would not 

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

 is the case in so many Echinoid larvae 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 species d in comparison with that of species b. The idea of 

 the identity of species a and c, or of species b and d then evidently must 

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

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

 Against the idea that these larvae might belong to Echinoneus and Rhyn- 

 cholampas the fact also speaks that the larva of Oligopodia (Echinobrissus) 

 recens is of the type of the Clypeastroid larvse (comp. below), so that it 

 is highly improbable that the closely related Rhyncholampas should have 

 a larval form so entirely different. 



That the Echinopluteus transversus might belong to some Spatangoid is 

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



