HAWAIIAN AND OTHEE PACIFIC ECHINI. 



Collected by the U. S. Fish Commission Steamer Albatross, Commander 

 Chauncey Thomas, U. S. N., Commanding, in 1902 and Lieut. Com- 

 mander L. M. Garrett, U. S. N., Commanding in 1906. 



SPATANGINA Jackson. 

 General Characteristics. 



It must be admitted that the Spatangina do not make up a monophyletic 

 group equivalent to the Clypeastrina. The name is used here, as it was by 

 Jackson, to include all those Echini of the Exocycloida which do not belong in 

 either the Holectypina or Clypeastrina. From how many ancestral stocks 

 this group has sprung, we are not yet in a position to say. Hawkins, in his 

 most interesting and valuable paper, on the Holectypoida (1912, Proc. Zool. Soc. 

 London, p. 493) expresses the opinion that there are no fewer than four distinct 

 branches combined in this highly artificial group. My own impression is that 

 probably three lines of descent are concerned, but it is quite possible that we 

 are exaggerating differences and that in reality only two essentially different 

 stocks have contributed to the Spatangina. In that case it will be easy to 

 adapt our classification to the facts. 



The Spatangina are easily distinguished from all other Recent Echini by 

 the entire absence of a lantern or any trace of jaws. The occurrence of jaws 

 in very young Echinoneus (see A. Agassiz, 1909. Amer. Journ. Sci., ser. 4, 28, p. 

 490) only serves to emphasize this fundamental character. Aside from this the 

 mouth and peristome exhibit notable diversity in form and position. The peri- 

 stome may be circular, pentagonal, elongate-ellipsoidal, or oblique but is usually 

 transversely longest and more or less reniform. The remarkably regular and 

 characteristic arrangement of ambulacral plates around the peristome, discov- 

 ered by Loven by which la, Ila, Illb, IVa and Vb are always larger than 

 their companion plates and have two pore-pairs instead of one, requires no 

 comment other than to say that there seems no exception to this rule. In 

 most Spatangina, the peristome is distinctly anterior, and it may even be 



