) 



COLLECTION OF RAD I ARIA. 527 



ber of varieties in the collection. There are 

 thirty-seven species of asterias which occupy 

 twenty-seven frames. The lobes of some of them 

 are so very short as hardly to surpass the disk, 

 as is seen in the ast. discoidea, rosacea and cal- 

 car; but they are long in the greater number. 

 The most common species on our coasts is the 

 a. rubens. We shall also point out the a. helian- 

 thus and the a. echinites. 



The echinides, otherwise called urchins, have a 

 calcareous shell covered with long spines, which 

 are sometimes articulated, and fixed upon move- 

 able tubercles. This shell is pierced with a great 

 number of small holes, from each of which issues 

 a tube or retractile sucker, through which the 

 animal breathes ; they are regularly set, and have 

 been named ambulacra; sometimes they extend 

 all round the body and sometimes only over a 

 part: their number, their form, and the respec- 

 tive position of the two intestinal canals, serve 

 to characterize the eleven genera of this section. 

 The very complicated apparatus of the mouth of 

 the urchins has been named lanthorn. We may 

 here see a specimen of the whole apparatus as 

 well as of its several parts. The echinides feed 

 on small shell fish. There are one hundred and 

 seven species in the collection : among which we 

 shall particularly notice the scutella latissima; 



