STRONGYLOCENTROTUS. 353 



than nudus. The recently described fragilis Jackson from off the coast of Cali- 

 fornia, although obviously related to drobachiensis, seems to be fully entitled 

 to recognition. 



The following table will show the most important characters for distinguish- 

 ing the species herein recognized: 



Pore-pairs 4-7 in each arc, only very exceptionally 8. 



Poriferous areas very broad, with pore-pairs in arcs of 4 which are nearly hori- 

 zontal at ambitus, with pore-pairs well separated so that they form 4 vertical 



series, the two outer sometimes crowded together pulcherrimus. 



Poriferous areas not as above. 



Gill-cuts deep and sharply defined. 



Test not depressed, v. d. rarely less than .50 h. d. and usually more than 



.66 h. d. ; actinal surface not flat granularis. 



Test depressed, v. d. usually less than .4.5 h. d.; actinal surface very flat depressus. 

 Gill-cuts neither deep nor sharply defined. 



Pore-pairs 4-6, sometimes 7; abactinal primary tubercles small; primary 



spines short or moderately long; color rarely very dark. 

 Test very thin and fragile, depressed, v. d. less than .50, sometimes 

 only .33 h. d.; auricles high, slender, racquet-shaped; spines ex- 

 ceedingly slender and fragile, bright reddish orange at base, with 



more or less of tip whitish fragilis. 



Test and spines not as above. 



Coronal plates very few; 11 interambulacral plates in each col- 

 umn in a specimen 30 mm. h. d., 15 in 60 mm. specimen . . sachalinicus. 

 Coronal plates much more numerous; 14 interambulacral plates 

 in a column in 17 mm. specimen, 28 in a 56 mm. specimen. 

 Pore-pairs typically 5, sometimes 4, rarely 6. 



Poriferous area much wider than half interporiferous, 

 the arcs nearly horizontal at ambitus, with pore-pairs 

 tending to form three vertical series, inner with two, 

 median with one and outer with two (rarely 3) pore- 

 pairs; primary spines greenish or reddish or both; 

 valves of globiferous pedicellarise with terminal 



tooth not half as long as blade intermedius. 



Poriferous area about equal to half of interporiferous, 

 the arcs very oblique at ambitus, the pore-pairs, 

 forming only an inner series of two and an outer series 

 of three; primary spines light violet tipped with 

 white, the actinal ones often faintly banded; valves 

 of globiferous pedicellariEe with a short blade and 



terminal tooth nearly as long pulchelluf;. 



Pore-pairs typically 6, often 7, very rarely 8. 



Primaries moderate, 10-15 mm. long or more; inter- 

 ambulacral plates 18-23 in each column; color 

 not uniform dull rose-purple. 

 Pore-pairs 6 in an arc, in the mid-zone, occasion- 

 ally 7; arcs horizontally oblique; abactinal 



