LECTURE X: 
151 
of the mouth, and differing in number in the dif- 
ferent species. I should not omit to observe that 
the curious species last mentioned, the Medusa’s, 
Head Star-Fish, is chiefly confined to the Indian 
seas, but is sometimes found in those of Europe. 
Those who may wish for a particular description 
of the anatomy of the Star-fishes, may consult the 
observations of Reaumur on this subject, publish- 
ed in the Memoirs of the French Academy. 
The concluding genus of the Linnaean Mollus- 
ca Nuda, or such as have not a true shelly inte- 
grant, is called Echinus or Sea-Urchin. Its ap- 
pearance is remarkable, the body, which is soft, 
being inclosed in a thin, calcareous crust, which 
is thickly beset with spines, of different length in 
the different species, which are extremely numer- 
ous, and vary considerably in habit or general 
appearance from each other. The mouth in this 
genus is central, placed beneath, and furnished 
with five strong, converging, bony teeth or spines. 
The most familiar example of the genus is the 
common or edible Sea-Urchin ; the Echinus escu- 
lentus of Limiceus, so very frequently seen on 
many of our own coasts. Its shape is nearly glo- 
bular, but slightly flattened beneath, and some- 
