208 bulletin: museum of comparative zoology. 



north of the equator. Numerous fossil Cidaridae from Tertiary, Cretaceous, 

 Jurassic, and possibly even Triassic strata are to be referred to either this geuus 

 or the preceding. The following key is based on the examination of 536 speci- 

 mens, representing all of the living species, except nuda. 



Key to the Species. 



Primary spines more or less white and smooth, rarely conspicuously gran- 

 ular, prickly, or ridged, and neither flaring nor conspicuously flattened 

 at tip ; median ambulacral area less than .50 of ambulacrum and almost 



wholly covered with small tubereles abyssicola 



Primary spines more or less prickly, granular, or ridged. 



Each coronal plate with only a few tubercles on inner half (generally 

 less than 25, not counting scrobicular circle) ; sutural line of ambu- 

 lacra usually distinctly visible; each ambulacral plate with I or 2, 

 seldom 3, tubercles ; primaries more or less cylindrical, often flar- 

 ing at tip, and never conspicuously flattened there ; median inter- 

 ambulacral area less than .25 of interambulacrum in width ; sutural 

 line usually quite distinctly sunken and bare. 

 Whole abactinal surface well covered with light-colored secondary 



and miliary spines papillata 



Whole abactinal surface appearing noticeably bare from small number 

 of secondary and miliary spines present ; test light-colored, but all 



spines reddish-brown or purple nuda 



Each coronal plate with numerous (more than 30) tubercles on inner half ; 



sutural line of ambulacra often not visible, each plate with 2-5 



tubercles. 



Median interambulacral area less than .25 of interambulacrum ; sutural 



line quite distinct; abactinal system with numerous tubercles 



(genital plate with 110±; ocular with 30±); primaries often 



flattened near tip, sometimes greatly expanded into broad flat 



fans blakei 



Median interambulacral area often more than .25 of interambulacrum ; 

 sutural line well concealed by tubercles ; abactinal system with 

 rather few, large tubercles (genital plate with 55 ±5 ocular with 

 20 ±); primaries terete, covered with sharp granules and never 

 either conspicuously flattened or flaring at tip rugosa 



Doroeidaris abyssicola. 



Dorocidaris abyssicola A. Agassiz, 1809, Bull. M. C. Z., 1, p. 253. 

 Plate 1, figs. 1-4, Rev. Ech., A. Agassiz, 1873. 



This species seems to be quite distinct from papillata, and while it is occa- 

 sionally much like blakei or rugosa in certain features of the test, the primaries 

 commonly distinguish it from either of them at a glance. In addition to the 

 characters given in the key may be mentioned the following: the abactinal sys- 

 tem is very large (.48-.S5 h. d.), while the actinostome is relatively quite small 

 (.35-. 45 h. d. but only -70-.80 of the abactinal system) ; the test is usually under 



