SPIRULA. 



517 



tucket. The shell is white and pearly, coiled up in two 

 or three turns, which do not touch each other, some- 

 thing like a ram's horn. The suriace exhibits constric- 

 tions, at short intervals, each of which corresponds to 

 an internal partition, so that the whole shell is divided 

 off into chambers, having a tube, however, at one side, so that the 

 whole arc in communication. ( Gould.^ 



The specimen figured is from the cabhiet of E. R. Mayo, Esq. 

 It is from Nantucket. 



S.fragilis. 



