CLARK: THE CIDARIDAE. 217 



of material is available for comparison that such individuals cau be properly 

 placed. Unfortunately in preparing the following key there have been available 

 only five species, represented by 69 specimens, and it is probable that errors have 

 crept in which might have been avoided had a larger series of specimens been 

 available. However, Anderson's and Doderlein's descriptions and figures are 

 sufficiently complete and accurate to make it possible to include their species. 

 Doderlein's ( : 06) measurements and figures have been of the greatest help. 

 The Japanese species need revision based on plenty of material, and it is possible 

 that the three species here recognized will prove to be simply forms of a single 

 species, as the differences between them are slight. All the recent species occur 

 in depths of 40 fathoms or over, and all but one (ingolfiana) are found only in the 

 Indo-Pacific region. A number of fossil species from the Cretaceous are referred 

 to this genus. How Doderlein (: 06) can lay great stress on the form of the 

 pedicellariae in Stereocidaris and write without qualification " Grosse und kleinere 

 globifere Pedicellarien ohne unpaaren Endzahn" (p. 102), is incomprehensible, 

 for his own figures (Plates XXXVI and XXXVII) contradict the statement flatly. 

 Had I examined no specimens, the study of Doderlein's figures would have satis- 

 fied me that the pedicellariae are no more reliable than the spines. 



Key to the Species. 



Actinostome very small, .20-.35 h. d., usually under .30 except in young 

 specimens. 

 Primary spines often more or less trigonal, but seldom with three con- 

 spicuous " wings " near base ; tridentate pedicellariae wanting ; 

 pedicels contain perforated plates besides thorny curved rods. 

 Longest primary spines, 1.3-2.7 h. d., thickness commonly less than 

 8% of length; perforated plates in pedicels small, with few large 



holes indica 



Longest primary spines about 1.35 h. d., thickness about 10% of length; 



perforated plates in pedicels broad, with many small holes . . . capensis 

 Primary spines commonly with three conspicuous wings near base ; 

 tridentate pedicellariae common ; pedicels with few or no per- 

 forated plates tricarinata 



Actinostome larger, almost always over .35 h. d. 



Primaries pale pink or reddish, with 10-16 longitudinal series of fine 

 prickles, which often merge into ridges, and 1 (or more) of these 

 becomes a conspicuous " wing" or "buttress " on basal half of spine, 

 which is also often flattened ; primaries tapering towards tip ; coronal 

 plates 5 or 6 (rarely 7). 

 Abactinal system coarsely tubercled ; median ambulacral area de- 

 pressed and bare along vertical suture, each plate with only 1 or 

 2 tubercles; color of test and secondaries madder purple . . . alcocki 

 Abactinal system with numerous small tubercles ; median ambulacral 

 area not depressed, often elevated along vertical suture, which is 

 seldom visible, crowded with tubercles, each plate with 4-6 ; color 

 of test and secondaries brownish, usually very pale ; no tridentate 

 pedicellariae ingoljiami 



