HAWAIIAN AND OTHER 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. 



PEDINID^E Gregory. 

 GENERAL CHARACTERISTICS. 



IT is quite remarkable that the recent species of this family represent but a 

 single genus and, with one exception, are very much alike in all essentials. The 

 solid spines, the firm test, and the bright colors make their resemblance to the 

 Echinidse rather striking but the grooved teeth and the perforated tubercles 

 indicate a nearer relationship to the Centrechinidse. 1 On the other hand we find 

 such peculiarities in the alimentary canal and abactinal system that it is an open 

 question whether the relationship to the Centrechinidse is really as close as it 

 seems. Yet it must be admitted that the resemblance of the recent species of 

 Csenopedina to Centrostephanus, particularly to C. longispinus, is very close 

 and it is extremely difficult to draw the line so sharply as to warrant their being 

 placed in separate families. The structure of the ambulacrum, the perforation 

 of the primary tubercles, the plating of the buccal membrane and the appearance 

 of the lantern are identical in the two genera, while the abactinal system and the 

 pedicellarise of Csenopedina are so similar to those of Centrostephanus asteriscus 

 that no possible generic difference can be found in those characters. Indeed the 

 only distinct and constant differences are found in the primary spines (which are 

 ordinarily smooth and solid in Csenopedina, rough and hollow in Centrostephanus) 

 and in the primary tubercles (which are distinctly crenulated in Centrostephanus 

 but perfectly smooth in Csenopedina). The smaller spines of Csenopedina are 

 sometimes hollow however, and the larger primaries are, in C. hawaiiensis at 

 least, decidedly rough. Were it not for the large number of fossil forms known, 

 which seem to represent a different group from our modern Centrechinidse, the 

 family Pedinidss would not be either necessary or desirable, for Csenopedina 

 could well be referred to the Centrechinidse. But until a more complete revision 



1 For the use of this name, see Jackson, 1912, Phylogeny of the Echini. Mem. Boston Soc. Nat. 

 Hist., VII, p. 2728. The conclusion that Diadema cannot be used for Echini seems to be unavoidable. 



