232 HAWAIIAN AND OTHER PACIFIC ECHINI. 



much alike that they can be separated only with the greatest difficulty and I 

 am unable to regard them as really distinct species. ]Mortensen himself ("In- 

 golf" Ech., pt. 1, p. 140) recognizes the close relationship of these two forms 

 but considers it desirable to separate them in order to make the family defmitions 

 more precise. The difference in their globiferous pedicellarise, upon which 

 their position in different families is based, is so slight, that the comparison of 

 Mortensen's figures ("Ingolf " Exp., pt. 1, PI. 19, figs. 19 and 23) and the perusal 

 of Doderlein's paragraphs ("Valdivia" Ech., p. 232) in which ]\Iortensen's 

 course is defended, is suggested to any one interested in the matter. It is un- 

 fortunately necessary in systematic work to use lines of division wliich do not 

 exist in nature, and it must be frankly admitted that some of those emploj'ed 

 here are open to serious criticism, but it is hoped that the separation of any two 

 closely allied forms upon such an utterly trivial basis as this which is supposed 

 to separate magellanicus and alhocindus has been avoided. Similar cases of 

 wide separation of forms which seem very closely allied are the cases of Strongylo- 

 centrotus lividus and drobachiensis, S. tuberculatus and franciscanus, and S. albus 

 and S. gibbosus. On the other hand, we find more or less close relationship 

 proposed between S. albus and Echinus microtuberculatus, between S. lividus and 

 the species of Echinus, between Sphcerechinus granularis and Tripneustes and 

 between Heliocidaris and the Echinometridae. All of these seem most improbable 

 if not impossible associations. In view of these striking cases it is not easy to 

 understand how Mortensen can express himself as he does (1. c, p. 140) concerning 

 the "natural relation" of his proposed groups. 



The second objection to Dr. Mortensen's system as applied to the Echinida? 

 is the inconsistency of relying on it for the greater part of the regular Echini 

 but failing to use it for the Tomnopleuridae. I can hardly do better than 

 quote Mortensen's own words on this point (Dan. Exp. Siam: Ech., p. 56): 

 "It is a very surjirising fact that the pediccUariic of the Temnopleurids prove 

 to ])c only of subordinate value for classification. * * * they mostly give only 

 specific characters. In the larger genera * * * the glol>iferous pedicellariie 

 assume tlie forms occurring botii in the Echinida?, Toxopncustidir and Echino- 

 motriche; in some species * * * they even occur in the same specimen in both 

 tli(^ two forms which distinguish the families Toxopneustida? and Echinometridrr. 

 This very curious fact, of course, does not alter the classificatory value of the 

 pedicellariir in the other regular echinids: but we are forced to seek the generic 

 characters of the Tenmopleurids in the structure of the test." The conclusion 

 which Dr. Mortensen reached for the Tenmopleurids. from his study of the 



