44 



ECHINOIDEA. I. 



From the specimens before me I am compelled to conclude, that the amount of calcification of the 

 plates is a point in which individuals living together may differ among themselves*. 



As another important difference between the two genera Wyv. Thomson (395) emphasizes 

 the fact that in Phormosoma the actinal side is very different from the abactinal side, while in Calvcria 

 (which is, according to Agassiz, synonymous with Asthenosoma] both sides are rather equal. This 

 character was excellent, as long as only the species described by Wyv. Thomson were known; but 

 it could not hold good with regard to the large number of new species brought to light by the 

 Challenger -Expedition. Agassiz has also several times declared, although only in an indirect way, 

 that the two genera cannot in reality be kept distinct In the Challenger* Echinids (p. 87) he says 

 of young specimens of Asthenosoma pcllucidum that they show how close is the relationship between 

 the genera Phormosoma and Asthenosoma in spite of the apparently great structural differences existing 

 between the adult of such species as Asthenosoma Grubei and Phormosoma luculentum. It is mainly 

 from the comparatively larger number of coronal plates in the former genus, that the young of the 

 two genera can be satisfactorily distinguished, the other characteristic features, the lapping of the 

 plates appearing only in larger specimens;). Of Phormosoma panamcnse Agassiz says (13. p. 77) that 

 it has on the actinal side the characters of Phormosoma most decidedly developed, while on the abac- 

 tinal side the great elongation of the ambulacral plates and the arrangement of the coronal plates 

 resemble the structural features of Asthenosoma^. 



Thus we have no fully reliable characters for the two mentioned genera. We have then to 

 choose between two alternatives: to make the whole one genus, or to search for better characters. 

 The first alternative is only a confession of incompetency ; we must try the second. It is beforehand 

 probable that good characters must be found, as these animals show so rich a variety of interesting 

 structures. The examinations have also in ample measure borne out the anticipations of finding good 

 characters. The arrangement of the tube feet, the structure of the spines, the spicules, 

 and above all the pedicellarise, yield most excellent characters, as well with regard 

 to genera as to species. The old genera Phormosoma and Asthenosoma prove to be 

 highly heterogeneous; several new genera will have to be established. 



Besides the rich material of the Ingolf-Expedition, and what was previously found in our 

 museum, I have examined the type specimens of all the new species from Challenger described by 

 Agassiz, to which species Prof. Bell most liberally granted me admission during my stay at British 

 Museum. Further Prof. Pfeffer has kindly sent me a couple of specimens of Asthenosoma variuvi 

 Grube for examination. Accordingly my examinations rest on a very broad base; with the exception 

 of Phormosoma hispidum, panamcnsc, Asthenosoma longispinum, lijamai, and Sperosoma biseriatum, I 

 have examined all known species, and of almost all of them the type specimens. 



As already mentioned, it is the spines, the pedicellarise, the tube feet, and the spicules, which 

 bear the principal part in the new classification of the Echinothurids that is the result of these 

 researches. Of course also the structure of the test is always of importance; but the all-predominant 

 importance that has hitherto been attached to the form and mutual relation of the plates, will have 

 to be very much reduced. In most Echinothurids the primary spines on the actinal side are provided 

 with a peculiar, hoof-shaped terminal cap, of a structure different from that of the other part of the 



