154 OUR COMMON BRITISH FOSSILS. 



of a remarkable egg-like shape. Archceocidaris is the 

 oldest known Cidaris, or knobbed sea-urchin, and it 

 occurs in the Devonian rocks ; but one species {A. 

 Urii) is not uncommon in the Carboniferous lime- 

 stone of the Derbyshire Peak district, and I have 

 found its spines somewhat plentifully in the queer 

 little limestone quarry at Hafod, near Corwen, in 

 North Wales. P alceecJmius seems to occur most 

 plentifully in the Carboniferous limestone of Ireland. 

 Some beds of the Inferior Oolite literally swarm with 

 fossil Cidarids and Cake-urchins. The slabs of Oolitic 

 limestone found in the quarries about Calne may be 

 seen containing a dozen Cidarids, many of them with 

 their spines still attached, just as when they were 

 alive. Leckhampton Hill, near Cheltenham (from the 

 summit of which the tourist can obtain a magnificent 

 view of the Severn valley), is composed of rocks 

 belonging to this formation in which Hypoclypeiis 

 agariciforme is abundant, as well as various species 

 of Cidaris. Hartwell, in Buckinghamshire, is another 

 good hunting-ground for fossil echinoderms. Clypetis 

 sinuata is a fine, large, well-known fossil, well dis- 

 tributed in the Lower Oolitic rocks ; it is, perhaps, 

 most abundant in Wiltshire. The Cotswold Hills 

 have numerous outcrops where quarries are opened 

 in their Oolitic rocks, in which Nticleolites, Cidaris, 

 and Hemicidaris are frequently very abundant. 



Speaking of the fossil Echini of Calne, Dr. Wright 

 says he has seen slabs from the beds of Coralline 



