BIGELOW : THE " GRAMPUS " IN THE GULF STREAM. 209 



latter there are only sixteen tentacles, though there are thirty-two canals, whereas in 

 S. nauarchus the number of tentacles equals that of canals or, since young tentacles 

 are formed before the corresponding blind canals, may be slightly greater. From 

 S. simulans, to which it is more closely related, it is separated by its greater size, 

 and by a larger number of tentacles and canals. It is, moreover, readily distin- 

 guished from both previously known species by the presence of the apical de- 

 pression of the exumbrella, as well as by the permanently blind terminations of 

 the centripetal canals. 



VOL. LII. — NO. 12 14 



