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 Nudct, 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 Linnaeus, so very frequently seen on 

 many of our own coasts. Its shape is nearly glo- 

 bular, but slightly flattened beneath, and some- 



