ECHINOIDEA. 



39 



daris); in others the rows of pores are doubled (=Diploci- 

 daris). The genus Hemicidaris (fig. 8, 4 ), distinguished by 

 the large spine-bearing tubercles on the lower part of the 

 ambulacra, ranges from the trias to the chalk-marl. Diademce, 

 with smooth, solid spines ( = Hemidiadema), appear in the 

 lias, and continue to the chalk, where the modern type, with 

 annulated, hollow spines, appears. Echinopsis, most common 

 in the chalk and older tertiaries, also occurs in the lias. 

 Acrosalenia, a genus characteristic of the oolites, is distin- 

 guished from Salenia by its perforated tubercles. Acrocidaris, 

 Heliocidaris, and several other sub-genera of Echinus, are also 

 peculiar to the oolites. Glypticus, chiefly there represented, 



Echinidce ; Spatangidce. 



1. Paleechinus sphjericus, Scouler ; Carboniferous, Ireland. 



2. Archaeocidaris Urii, Flern. ; Carboniferous, Ireland. 



3. Cidaris glandifera, Goldf. (spine); Jura, Mount Carrnel. 



4. Hemicidaris intermedia, Flem. ; Corallian, Calne. 



5. Salenia petalifera, Desm. ; U. Greensand, Wilts. 



6. Disaster ringens, Ag. ; Inferior Oolite, Dorset. 



7. Hemipneustes Greenovii, Forbes ; U. Greensand, Blackdown. 



8. Catopygus carinatus, Goldf. ; U. Greensand, Wilts. 



has one species in the chalk of Ciply. Salenia (fig. 8, 5), 

 with its ornamental disk, is characteristically cretaceous. 

 Arhacia and Temnopleurus appear first in the eocene. The 



