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 definitions 

 more precise. The difference in their globiferous pedicellariae, 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 Mortensen'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 which do not 

 exist in nature, and it must be frankly admitted that some of those employed 

 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 albocinctus has been avoided. Similar cases of 

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

 centrotus Hindus 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 microtubcrculatus, between S. lividus and 

 the species of Echinus, between Splicer echinus granularis and Tripneustes and 

 between Heliocidaris and the Echinometridao. 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 Echinidse 

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

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

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

 "It is a very surprising fact that the pedicellarise of the Temnopleurids prove 

 to be only of subordinate value for classification. * * * they mostly give only 

 specific characters. In the larger genera * * * the globiferous pedicellarise 

 assume the forms occurring both in the Echinida?, Toxopneustidse and Echino- 

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

 the two forms which distinguish the families Toxopneustidae and Echinometridae. 

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

 pedicellariae in the other regular echinids; but we are forced to seek the generic 

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

 which Dr. Mortensen reached for the Temnopleurids, from his study of the 



