ECHINOIDS: CIDARID.E. 



501 



Regular Echinoids have the mouth below, vent above, 

 both central, and the ambulacra in five pairs continuous 

 from vent to mouth ; ovaries five, and the mouth fur- 

 nished with a complicated dental apparatus. They are 

 from an inch to three or four inches in diameter, and dif- 

 ferent species have spines from a fraction of an inch to 

 three or four inches in length. 



CIDARID/E, OR CIDARIS FAMILY. This Family em- 

 braces echinoids which have the interambulacral areas 

 composed of two rows of plates. The Genera Cidaris, 

 Leiocidaris, Goniocidaris, Diadcma, Savignya, Astropyga, 

 EcJdnocidaris, Psammechinus, Echinus, Tripneustes, Bole- 

 tia, SpJuzrecJiimis, Toxopneustes, Heliocidaris, LoxccJdmts, 

 Echinometra, Acroladia, and Podophora, are among the 

 principal ones. Cidaris, Echinomctra, and Tripneustes are 

 found on the coast of Florida ; Echinocidaris, coast of 

 South Carolina and island of Naushon ; Toxocidaris, of A. 

 Agassiz, San Francisco ; Toxopneustes, both coasts of the 

 United States, North ; LoxccJiimis, Sari Francisco ; and 

 Psammechinus or LytecJiinns, South Carolina and Florida. 



The Irregular Echinoids have the mouth below, the 

 vent sometimes below, sometimes at one side, and the am- 

 bulacra not continuous. Fig. 4 s s . 



EcHiNONimE. This 

 Family has the ambulacral 

 areas simple, and a masca- 

 tory apparatus. EcJiino- 

 nc2is is the principal ge- 

 nus. 



CLYPEASTRID^E. This 

 Family contains those 

 which have the ambulacra 

 petaloid, and peristome 

 central. The GeneraZf^/fo'- 



_ . . Echinarachnius panna, Gray. Northeast 



nocyamns, Monhnia, La- coast of the United states. 



