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ECHINOIDEA. I. 



The same form of globiferous pedicellarite is found in Strongylocentrofats , Anthocidaris, and 

 Parasalcnia. The two former are distinguished by the globiferous pedicellariae having a well devel- 

 oped neck, provided with circular and longitudinal muscles an otherwise unknown feature. These 

 three genera are likely to be rather nearly related; their spicules, however, show that the relation 

 is not very close. In Strongyloccntrotus the spicules are a little branched in the ends, but otherwise 

 the original form is bihamate; in some species only (?) common bihamate spicules are found. In 

 Anthocidaris the spicules are biacerate, pointed in both ends and with a branch in the middle. A 

 somewhat similar form of spicules is found in Parasalenia; but in this genus the globiferous pedicel- 

 larise have no neck. Thus this latter seems to form a special group; its obliquity and the peculiar 

 anal plates indicate also that it must be interpreted as an aberrant form, of which the nearest, 

 although not very near, relations are: Anthocidaris and Strongyloccntrotics. In the genera Heliocidaris, 

 Echinostrephus, Toxocidaris, Echinometra, Heteroccnlrotus, and Coloboccntrotus there is a strong, unpaired 

 lateral tooth on the globiferous pedicellariae, and they have all simple bihamate spicules. Heliocidaris 

 occupies a somewhat isolated position; its globiferous pedicellariae are not so much developed as those 

 of the other genera, it reminds to a rather high degree of Stcrcchinus Neumayeri, but especially of 

 Pscudechinus albocinctus; several things favour the belief that Pseudechinus is really a transitional 

 form between Sterechinus and Heliocidaris, and the latter leads on again to Toxocidaris, Echiiioinetra 

 etc Thus we have here a very fine series of development where, together with the peculiar develop- 

 ment of the globiferous pedicellarise, a marked tendency to obliquity is seen, reaching the climax in 

 the genera Heterocentrotus and Colobocentrotus. There seems to be no occasion to separate these two 

 genera as a special group on account of their longitudinal axis not being placed in the same direc- 

 tion as in Echinometra, because their pedicellariae and spicules are exactly agreeing with those of 

 Echinometra. It is constantly seen that spicules and pedicellarise are the most important systematic 

 characters, so that there is no reason for suddenly following a new principle here. The genera Pseud- 

 echinus, Heliocidaris, and Echinostrephus must then be interpreted as more or less primitive oligopore 

 Echinometrids. 



Stomopneustes occupies a quite isolated position; its globiferous pedicellarise and spicules are 

 so peculiar and so different from what is found in the other forms mentioned here, that there can be 

 no question of classing it with any of them; it forms a special group. 



The relation between these forms may most easily be surveyed in the following diagram. For 

 safety's sake I shall expressly remark, however, that I do not mean it to be regarded as a phyloge- 

 netic one. I will in no way maintain that our Parechinus is the ancestral form of Echinus etc., but 

 only express my opinion that it shows the simplest structure of the (organs most important with regard 

 to classification. We may in the recent forms scarcely find more than an indication of the way the 

 development seems to have taken. Now there is unfortunately only a small chance of finding these 

 fine structures in the fossil forms, so we shall hardly get so far as to be able with certainty to point 

 out the ancestral forms. Otherwise this survey of the relations of the forms shows clearly that here is 

 everywhere a tendency to increase the number of tube feet, a development from oligopore to polypore 

 forms. The most original feature, no doubt, is that all the ambulacral plates are well developed with 

 primary spine and three tube feet; then the primary spines disappear from every other ambulacral 



