504 RADIATES I ECH1NODERMS. 



are merged in one ; and they vary in size from an inch or 

 two to a foot Or more in diameter. -Star-fishes have a 

 wonderful power of reproducing lost parts ; if an arm be 

 broken off, 'another soon grows in its place. Even after 

 all the arms but one have been destroyed, a star-fish has 

 lived, and new arms have sprouted out in the places of 

 the lost ones. They are common on almost all coasts. 



Miiller and Troschel divide the Star-fishes into three 

 groups. The first contains those which have four rows 

 of suckers, as Asteracantliion including Uraster ; the sec- 

 ond, those which have two rows of suckers, as Echinasttr 

 including Asterias and Cribella, Solaster, Chcetaster, Ophi- 

 diastcr, Dactylosaster, Tamaria, Cistina, Scytaster, Culcita, 

 Astericus including Asterina and Palmipes, Ptcrastcr, Ore- 

 aster, Astrogonium, Goniodiscus, Stellaster, Astcropsis, and 

 Archaster; the third, those which have two rows of suck- 

 ers, and no vent, as Astropecten, sEnodiscus, and Luidia. 



SUB-SECTION IV. 



THE ORDER OF OPHIURIOIDS, OR OPHIURANS. 



THIS Order embraces echinoderms which have the cen- 

 tral disk very small in comparison to the size of the arms, 

 Fig- 489- and circular ; and the 



arms start off abruptly 

 from its circumference. 

 Locomotion is effected 

 by means of spines. 



Miiller and Troschel 

 divide the Ophiurans in- 

 to two groups, Ophi- 

 urae and Euryalae. 



The Ophiurae are char- 

 acterized by simple arms, 

 , ophwphoiis. and contain the Genera 



Ophioderma including Ophiura, Ophiocnemis, OpJiiolcpis, 



