ECHINODERMATA., 951 
Fie. 208.—Ophiocoma Russet, an Ophiura; natural size. West Indies. 
abound on every shore, and are often seen at low tide half 
buried in the sand, or slowly gliding over the rocks. Cold 
fresh water is instant death to them. They have the pow- 
er of reproducing lost parts to a high degree. They are 
very voracious, and are the worst enemies of the Oyster. 
About 150 species are known. These may be divided 
into three groups: (1) species having four rows of feet, 
represented by the common five - fingered Asterias ; (2) 
species having two rows of feet, as the many-rayed Solas- 
ter, or “Sun-fish,’ and the pentagonal Goniaster; (8) 
species having long slender arms, which are not prolon- 
gations of the body, and are not provided with suckers, 
as the Ophiura, or “Brittle - star,” and Astrophyton, or 
“ Basket-fish.” The last are of inferior rank, and resem- 
ble inverted stemless Crinoids. The digestive sac is con- 
fined to the disk; and the madreporic plate is underneath. 
