30 



ECHINOIDEA. 



Taking these general principles for my guidance, I subdivide the Echinoidea into 



the followins: thirteen natural families 



Order— ECamOlDE A. { 



Echinoidea endocyclica. 



Vent within the genital plates, 

 always opposite the mouth. 



Echinoidea exocyclica. 



Vent without the genital plates, 

 never opposite the mouth. 



Cidaridse. 



Hemicidaridse. 



Diademadse. 



Echinidae. 



Salenidse. 



Echinocouidse. 



Collyritidse. 



Echinonidse. 



Echinobrissidse. 



Echinolampidae. 



Clypeasteridse. 



Echinocoridse. 



Spatangidse. 



Famili/ \. Cidarid^. — ^Test thick, spheroidal; iiiter-ambulacral areas very wide; 

 primary tubercles large, perforated ; bosses crenulated or uncrenulated, spines large, 

 thick, mostly claviform ; ambidacral areas very narrow ; poriferous zones narrow, pores 

 nnigeminal, rarely bigeminal ; mouth-opening large, inferior, central, circular or penta- 

 gonal ; peristome destitute of notches, always armed with large, powerful jaws. Vent- 

 opening wide, superior, opposite the mouth, surrounded by five large genital plates 

 perforated for the ovarial canals, and five small ocular plates excavated for lodging the 

 eyes ; buccal and anal membranes covered with scales. 



Types. Cidaris clavigera, Ktinig (PI. IV). Cidaris scepfrifera, Mantell (PI. VI). 



Family 2. Hemicidarid^. — Test thick, spheroidal, or more or less depressed ; ambu- 

 lacral areas narrow or wide, with semi-tubercles at their base only, or extended throughout 

 the area ; inter-ambulacral areas with two rows of primary tubercles, rarely more than 

 eight in each row ; tubercles of both areas perforated, and bosses deeply crenulated ; 

 poriferous zones narrow and undulated ; pores unigeminal throughout, except near 

 the peristome, where they are bigeminal and trigeminal. Mouth-opening large ; peristome 

 decagonal, and divided more or less deeply by notches into ten lobes ; jaws large and 

 powerful ; apical disc small, opposite the mouth, composed of five genital and five 

 ocular plates. Spines long, thick, cylindrical, tapering, claviform, or stout, compressed, 

 or angular; surface smooth, or covered with fine longitudinal lines, as far as known, 

 neither prickles nor asperities are developed thereon. 



Types. Hemicidar is intermedia, Fleming. Acrocidaris formosa, Agassiz. 



Family 3. Diademad^. — Test thin, circular, or pentagonal, more or less depressed ; 



