ECHINID^. 231 



which were supposed to distinguish atropurpureus have any real systematic 

 significance. 



Stomopneustes has not been recorded from the northern Pacific Ocean, nor 

 did the "Albatross" find it in either Hawaiian or Japanese waters. 



Agassiz. 

 GENERAL CONSIDERATIONS. 



There can be little reason to doubt that the EchinidsB are the present-day 

 representatives of the stock from which in the past the Temnopleuridse, Strongy- 

 locentrotidse, and Echinometridse have been derived. Indeed the relationship 

 with each family is so close that it is impossible to fix a natural boundary, passing 

 which no exceptions will be found. It is necessary therefore to choose between 

 fixing arbitrary lines and the alternative proposition of uniting all four groups in 

 a single family. The real interrelationships of the regular Echini are much 

 better shown by following the former course. The question then arises as to 

 the characters for distinguishing the groups. As in the case of the families 

 hitherto treated, the test furnishes the characters of morphological significance. 1 

 Mortensen (1903, "Ingolf" Ech., pt. 1 and 1904, Dan. Exp. Siam: Ech.) has 

 chosen the pedicellarise as the chief source for light on the relationships of these 

 Echini, and his lead has been followed by some other students of the group. 

 It is not altogether strange that my results differ greatly from his, and it is to be 

 regretted that they cannot be brought into something more nearly like harmony. 

 But in addition to the objections previously urged against the use of the pedicel- 

 larise as a factor of primary importance in classification, study of the Echinidse 

 and their allies has suggested two others which are of special weight in connection 

 with these forms. 



The first important objection to Mortensen's system is the separation which 

 results, of species obviously and by all the characters of the test very closely 

 allied, and the union of species, which it seems impossible to associate together. 

 To illustrate this objection the placing of Echinus magellanicus Phil, and E. albo- 

 cinctus Hutton in separate families, may be mentioned, although the two are so 



1 This was written before the publication of Jackson's magnificent monograph on the Phylogeny 

 of the Echini (Mem. Boston Soc. Nat. Hist., VII, 1912) in which the same course is followed. The 

 classification used herein is essentially identical with that to which he has been led by his prolonged 

 morphological studies. 



