44 ECHINOIDEA. I. 



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

 piates is a point in which individuals living together mav differ among themselves . 



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

 the faet that in Phonnosouia the actinal side is very different from the abactinal side, while in Calvcria 

 (which is, according to Agassiz, synonymons with Asfhenosoma) both sides are rather eqnal. 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 nnmber of new species brought to light bv the 

 «Challenger»-Expedition. Agassiz has also several times declared, althongh onlv in an indirect way, 

 that the two genera cannot in realit>- be kept distinct. In the «Challenger Echinids (p. 87) he savs 

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

 the genera Plwrmosoma and Asf/iriiosoma in spite of the apparently great structural differences existing 

 between the adnlt of snch species as Asthcnosovia Gnibcl and P/ionnosoiiin Incnlciifuiii. It is mainlv 

 from the comparatively larger nnmber of coronal piates in the former genus, that the young of the 

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

 piates appearing only in larger specimens. Of Phormosovia panamensc Agassiz savs (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 piates and the arrangement of the coronal piates 

 resemble the structural features of Asthcnosovia \ 



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 pedicellariæ, yield most excellent characters, as well with regard 

 to genera as to species. The old genera Phormosoma and Asthenosonia 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 t)-pe 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 Asfhenosoma varium 

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

 oi Phormosoma hispidum^ panamensc, Asthenosoma longispinum , lijamai, and Spcrosoma biseriatuiii , I 

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



As already mentioned, it is the spines, the pedicellariæ, 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 mntual relation of the piates, will have 

 to be very much reduced. In most Echinothurids the primar\- 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 



