120 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Anal snout not very prominent; greatest height of test far back; labrum usually 

 in contact with following interambulacral plate hirsutus. 



Anal snout very prominent; greatest height of test j ust back of middle ; labrum 



separated by ambulacral plates from following interambulacral cinctus. 



Plexechinus nordenskioldi. 



Mortenson, 1905. Vid. Med. f. 1905, p. 242. 



This Antarctic species was taken at the very moderate depth of 89 fms. 

 by the Swedish South Polar Expedition and has been fully described by Morten- 

 sen in his report on the Echini of that Expedition. 



Plexechinus hirsutus. 



Mortensen, 1905. Vid. Med. f. 1905, p. 242. 



This Arctic species was taken by the Ingolf at depths ranging from 485 

 to 1300 fms. It is much nearer the following species than it is to the preceding. 



Plexechinus cinctus. 



A. Agassiz, 1898. Bull. M. C. Z., 32, p. 76. 



Plate 145, figs. 3-6. 



This is the tropical species of the genus and was taken by the Albatross 

 in the Gulf of California at a depth of 676 fms. The pedicellariae are more 

 like those of hirsutus than they are like those of the Antarctic species, but the 

 tridentate are very characteristic. These have valves (PI. 145, fig. 6) about 

 .66 mm. long, with the blade narrow, somewhat compressed and coarsely den- 

 tate at tip. The ophicephalous have valves (PI. 153, fig. 3) onlj T about .12 mm. 

 including the loop. The rostrate (or globiferous, as Mortensen calls them) 

 are very similar to those of hirsutus; the valves (PI. 153, figs. 4, 5) are only about 

 .16 mm. long, and the base is nearly that in width. 



Urechinus. 



A. Agassiz, 1879. Proc. Amer. Acad., 14, p. 207. 

 Type, Urechinus naresianus A. Agassiz, 1879. hoc. cit. 



Since the first description of these notable sea-urchins, some eight addi- 

 tional species have been added to the genus and the distinctions bj' which they 



