38 
SAGAETIAD^. 
Of foreign species the beautiful S. decorata (Dana), found 
in the Lagoon of Honden Island, is closely allied to our 
belh's. 
S. Fuegensis (Dana), from TeiTa del Fuego, a very fine 
species with rich yelloAV column and disk, and grass-green 
tentacles, has much in common with the subject of this 
article, but it has far more prominently the characters, that 
the tentacles are short, and spring isolatedly from the disk. 
S. impatiens (Dana) has the habit of elongating the 
column pillar-wise, and of variously constringing and writh- 
ing the body ; thus appearing to be intermediate between 
hellis and viduata. 
It seems to be through bellis and Fuegensis, that the 
genus Sagartia leads off to the curious Discosonia 
nummiforme of the Red Sea, in which the column 
has no appreciable height, the animal being a very 
thin, flat, circular plate, with the tentacles reduced to 
minute warts, arranged in groups which form radiating 
bands. 
Of native species S. parasitica and B. clavata present, in 
the expanded character of their disks, marked relations 
with hellis. But a still closer affinity exists between hellis 
and Aiptasia amaclia, in the characters both of the disk and 
of the column, as I shall notice more particularly when I 
come to describe the latter. 
It ought never to be forgotten that the order of sequence 
which we are compelled to adopt in treating of creatures 
in a book — that of placing each species between two others 
— can by no means express all their relations. Every 
species stands in the midst of many others, some closer to 
it, some more remote, to which it is linked more or less 
obviously. “ Ten or twenty links would often be insuffi- 
cient to express these numerous relations.” * To obviate 
* Cuvier. 
