346 CRETACEOUS ECHINOIDEA. 



lower portion encloses a calcareous nucleus. Pedicellarige capable (in the living state) of 

 seizing small bodies and passing them from one to the other. Movement of the animal 

 effected by the motion of the spines and the ambulacra! tubes. 



The EcHiNoiDEA. (including the Perischoechinidae) range from the Silurian to the 

 existing period, and are represented in the British Cretaceous formation by ten families 



(ClDARID^, DlADEMADiE, SaLENIAD/E, EcHINOTHURIDiE, EcHINICOKID^, EcHINONlD^, 



EcHiNOBRissiDiE, EcHiNOLAMPiD^, SpATANGiD^, and EcHiNocoRiD^), and givc thirty 

 Cretaceous genera in one hundred and thirteen species, and are divisible into one 

 PalEEozoic section, the Palechinoidea, with more than twenty rows of plates, and two 

 Mesozoic and Cainozoic sections, the Echinoidea endocyclica and the Echingidea 

 EXocYCLiCA, wfth twenty rows of plates. 



Section A.— EcMnoidea endocyclica, Wrigld (p. 29). 



Anal opening within the genital plates, always opposite the mouth. Jaws always 



present. 



The section includes six families : CiDARiDiE, HEMiciDARiDiE, Diadejiad^, 

 EcHiNiDiE, Saleniad^, and Echinothurid^, ranging from the Trias to the existing 

 period. Four families (Cidaridj*;, Diademad^, Saleniad^, and Echinothurice) are 

 represented in the British Cretaceous strata, and give eleven genera : Cidaris, Pseudo- 

 DiADEMA, Pedinopsis, Echinocyphus, Glyphocyphus, Cyphosoma, Peltastes, Gonio- 

 ?HORUs, Salenia, Cottaldia, and Echinothuria, consisting of fifty-nine species. 



Eamily I.— CIDARID^, Wright (p. 35). 



Test thick, spheroidal, generally depressed at the upper and under surfaces. Ambu- 

 lacral areas narrow, usually undulating, and destitute of primary tubercles. Interambu- 

 lacral areas wide, carrying a few large primary perforated tubercles. Poriferous zones 

 narrow ; pores generally unigeminal. Oral and anal openings large. Peristome desti- 

 tute of notches. Apical disc large, composed of five large, equal-sized, angular genital 

 plates, and five ocular plates. Jaws large. Primary spines long, massive, and more or 

 less cylindrical. Family ranging from the Trias to the existing period, and represented 

 in the British Cretaceous strata by one genus, Cidaris, with seventeen species (pp. 

 35—79). 



Genus 1.— Cidaris, Klein (p. 35). 



Test thick, more or less depressed. Ambulacral areas undulathig. Primary tubercles 

 few, rarely more than six iu a row. Miliary zones more or less wide. Pores of the 



