354 HAWAIIAN AND OTHER PACIFIC ECHINI. 



interambulacral areas well covered by secondary 

 tubercles with relatively few miliaries; color 

 more or less greenish with or without a violet 

 tinge, passing on the one hand into a violet test 

 with deep green spines, and on the other into 

 dull yellowish or light brown, with little trace of 



either green or violet drobachiensis. 



Pore-pairs 7 in an arc, in the mid-zone, occasionally 

 6; arcs vertically oblique; abactinal inter- 

 ambulacral areas with few secondaries but 

 closely covered with miliary tubercles, except 

 along the bare median line; color more or less 

 reddish white, darkest on abactinal interam- 

 bulacral areas, which may be deep reddish 

 purple; primaries light red or light green or both echinoides. 

 Primaries numerous, very short, 6-8 mm. long, scarcely 

 distinguishable from secondaries; interambulacral 

 plates 25 in each column; color uniform dull rose- 

 purple polyacattthus. 



Pore-pairs 6 or commonly 7; abactinal primary tubercles large and 

 conspicuous; primary spines long; color usually dark brown or 



purplish nvdus. 



Pore-pairs 8-10 in each arc. 



Pore-pairs 8; primary spines short; primary tubercles not conspicuous; globif- 



erous pedicellaria 3 common; color, when adult, purple purpuralus. 



Pore-pairs 9-10; primary spines long; primary tubercles large, in 6 conspicuous 

 series in each interambulacrum ; globiferous pedicellariae usually very few; 

 color commonly red-brown, rarely purple franciscanus. 



Strongylocentrotus fragilis Jackson. 



Strongylocentrotus fragilis Jackson, 1912. Mem. Boston Soc. Nat. Hist., VII, p. 128. 



Plates 94, figs. 28, 29; 113, figs. 3-6. 



As Jackson gives only a brief description of this fine species and leaves me 

 the privilege of figuring it, photographs of the type and of a smaller specimen 

 with spines are given, together with some notes on the structural characters. 

 A large series of specimens at hand ranges from 9 to 90 mm. in diameter; the 

 largest is 40 mm. high. A specimen 55 mm. h. d. is 26.5 mm. high, while another 

 38 mm. h. d. is only 12 mm. high. But these represent the two extremes and 

 the great majority of specimens are about two fifths as high as they are across. 

 The test is very thin and fragile, and the auricles are so high and slender, and 

 expand at the tip so much like a racquet, that they make a good specific 

 character. There are 5 (rarely 6) pairs of very large pores in each arc, and the 



