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 

 tingf, 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 hne; 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, &-8 mm. long, scarcely 

 distinguishable from secondaries; interambulacral 

 plates 25 in each column; color uniform dull rose- 

 purple polyacanthxis. 



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

 conspicuous; primary spines long; color usually dark brown or 



purplish nudus. 



Pore-pairs 8-10 in each arc. 



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



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



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

 scries in each interambulacrum; globiferous pedicellaria; usually very few; 

 color commonly red-brown, rarely purple franciscanus. 



Strongylocentrotus fragilis Jackson. 



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



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



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

 tlio pri\'iloge 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 rnngo-^; from 9 to 90 mm. in diameter; the 

 largest is 40 mm. iiigh. A specimen 5o mm. h. d. is 20.5 mm. high, while another 

 3<S nun. h. d. is only 12 mm. high. But these represent the two extremes and 

 the great majority of specimens are about two fifths a.*< high a^ they are across. 

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

 expand at the tip so nnich like :i racquet, that they make a good specific 

 character. There are 5 (rarely 0) pairs of very large jiores in each arc. and the 



