308 



ECHINODERMATA— ECHINOZOA 



PHYLUM IV 



Geological Range and Distribution of the Echinoidea. 



Fossil Echini make their first appearance in the Ordovician, but are then 

 represented .by but a single genus, Bothriocidaris, which on structural grounds 

 is a highly primitive type. In the Silurian of Great Britain occurs 

 the order Echinocystoida, and in the American Silurian, Koninckocidaris, first 

 of the Lepidocentridae. In the Devonian one possible Cidarid occurs in 

 Europe and a number of genera of the Perischoechinoida in Europe and North 



Fig. 435. 



Mcckechinus elcfians Jackson. Permian ; Grand Summit, Kansas. Dorsal \-iew of test with a distinct 

 madrt'porite and oilier apical ])lates, enlarged, 2/j. Lower left-hand figure, ambulacral plates with spines more 

 enlarged. Lower right-hand ligure segment of interambulacrum with spines .still more enlarged. Upper left- 

 hand figure, jiedicellaria much enlarged, *-'/i (after Jackson). 



America. In the Lower Carboniferous the Cidarids are represented by one 

 species of Miocidaris ; otherwise the whole Echinoid fauna is composed of the 

 Perischoechinoida, which order finds here its greatest development in genera 

 and species. 



