206 



also Coelopleurus may be got at without too- much trouble, while the rare, 

 small deep-sea forms Podocidaris, Habrocidaris etc. will, at any rate, not 

 be within easy reach. But the study of the two first named forms will 

 suffice for meeting reasonable claims to the knowledge of this larval 

 "family." 



It is, however, especially the larvae of the Camarodonta which we must 

 consider in discussing the classificatory value of the larvae. This great group 

 comprises the bulk of the recent regular Echini, and here the views of 

 the various authors regarding what would be a natural arrangement are 

 most diverging. May not perhaps the larvae give us the clue to their real 

 interrelations? We now know, more or less completely, the larvae of so 

 many of these forms that we are at least able to form a fair judgment, 

 whether the larvae will give us any support for the solution of the problem. 



Two main views regarding the classification of the Camarodonta are 

 prevailing among recent authors. One is that of H. Lyman Clark and 

 R. T. Jackson, the other that of Doderlein and myself. While according 

 to the two former authors the test structure alone affords valid characters 

 by which to distinguish genera and families, the minor microscopical struct- 

 ures, the pedicellariae and spicules affording characters of no higher value 

 than for distinguishing species, I have expressed the view that also the 

 microscopical structures, especially the globiferous peclicellarise, afford a 

 valid basis for the higher systematic divisions, the genera and even the 

 families, and that these characters should be taken into consideration as 

 well as the structural characters of the test. The latter characters are, of 

 course, regarded as the more important, but it is maintained that where 

 the structural characters of the test do not give the clue to the natural 

 interrelationship of the forms, as is mostly the case in the great and uni- 

 form group of the Camarodonta, there the microscopical characters set in. 

 The classification worked out on the base of these principles, which was 

 set forth in the author's work on the Echinoidea of the Danish "Ingolf"- 

 Expedition, Part I II. (1903 7) was fully accepted by Doderlein, who 

 is even inclined to ascribe still more importance to the microscopical 

 characters than I can agree to. In the said work I have especially 

 pointed out that the character of the ambulacra, the oligoporous or poly- 

 porous condition, is of no value as a character of larger groups, as it has, 

 evidently, developed separately in different groups. Also the elongation of 

 the test in Echinomdra and some allied genera is regarded as unvalid as 

 a family character. H. L. Clark on the contrary regards these two char- 

 acters as of primary value for the classification, although he cannot deny 

 that the polyporous condition has developed in at least two separate 

 groups (his families Strongylocentrotidae and Echinometridae). 



