ECHINOIDEA. I. 



The globiferous pedicellarise with the edges of the blade 

 thickened, connected by cross-beams across the inside (in 

 Ech. Alexandri^ however, sometimes without such cross- 

 beams) 5. 



4. The plates on the buccal membrane thick, greenish, of a 

 peculiar structure (a compact calcareous mass with deep, 



funnel-shaped holes); they form a dense covering Par echinus microtuberculatus (Blv. 



The plates on the buccal membrane not greenish, of 

 the common structure; they form no quite dense covering, 

 naked skin is seen between them Par echinus miliaris (Mull.). 



5. Primary tubercle on all the ambulacral plates 6. 



only on every other ambulacral plate... n. 



6. The tridentate pedicellarise with the blade broad and rather 

 flat; the globiferous pedicellarise generally with 34 teeth 



on either side of the blade Echinus Alexandri Dan. Kor. 



The tridentate pedicellarise with the blade narrow and 

 deep; the globiferous pedicellarise with i 2 teeth on either 

 side of the blade 7. 



7. The primary tubercles on the ambulacral areas of very- 

 unequal size, or, if the size decreases regularly towards the 

 apical area and the peristome, the two series in each 



ambulacral area of very different size Echinus a/finis Mrtsn. 



The primary tubercles on the ambulacral areas decrease 

 regularly in size towards the apical area and the peristome; 

 both series of equal size 8. 



8. The test high 9. 



rather flat 10. 



9. Finely red; the ophicephalous pedicellariae with uncom- 

 monly long blade Echinus atlanticus Mrtsn. 



With a fine green coloration; the ophicephalous pedi- 

 cellariae of the common form Echinus gracilis Ag. 



10. The globiferous pedicellarise generally with 2 2 lateral 

 teeth; the test and the spines generally finely red and 



white, more rarely the test violet Echinus elegans Dub. Kor. 



The globiferous pedicellarise generally with i i lateral 

 tooth ; the test and the spines white Echinus lucidus Doderl. 



11. Spines on the buccal plates; the primary spines short, 



thick, not distinctly longer than the secondary ones Echinus esculcntus L. 



No spines on the buccal plates; the primary spines 

 considerably longer than the secondary ones 12. 



