ECHINOIDSI CIDARUXB. 



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, Diadema, Savignya, Astropyga, 

 Echinocidaris, Psammechinus, Echinus, Tripneustes, Bole- 

 tia, Sphczrechinus, Toxopneustes, Heliacidaris, Loxechinus, 

 EcJiinometra, Acroladia, and Podophora, are among the 

 principal ones. Cidaris, Echinometra, and Tripneustcs 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 ; Loxechinus, San Francisco ; and 

 Psammechinus or Lytechinus, 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. 485. 



ECHINONIM:. This 

 Family has the ambulacral 

 areas simple, and a masca- 

 tory apparatus. Echino- 

 neus is the principal ge- 

 nus. 



CLYPEASTRID^:. This 

 Family contains those 

 which have the ambulacra 

 petaloid, and peristome 

 central. The Genera.V/zz- 



7i /r j- ' T Echinarachnius parma, Gray. Northeast 



nocyamus, Mouhma, La- coast of the united sL es . 



