HTDROIDA. BALE. 43 



The original example of this magnificent species is by far the 

 finest specimen of any Hydroid which I have met with. It 

 springs from a dense spongy mass of hydrorhizal filaments, 

 measuring about four inches in one direction by one and a half 

 in another, and two inches high to a point where it subdivides ; 

 the two divisions extending upwards for about thi-ee inches 

 further, around the bases of the two main trunks on which the 

 colony is borne. One of these trunks, before emerging from the 

 spongy mass, has already divided into half a dozen branches, 

 each averaging about 2| mm. in diameter; the other, which 

 commences to branch a little higher up, is about 9 mm. through. 

 The polypidom, which slightly exceeds two feet in height, is 

 branched und re-branched most exuberantly, and is bare only 

 near the base, the hydrocladiate portion forming a dense bush 

 about fifteen inches in lateral spread, and between two and three 

 inches through in the dried specimen. 



As in the last two species a pair of branches originates from 

 two successive internodes of the hydrocladiate tube, but they are 

 here much less divergent, rising at angles of as little as 20, 

 while they stand out in front in a plane of about the same angle. 

 Thus a branch of three or four inches in length may have about 

 three pairs, each of which lies in a plane cutting that of the 

 parent branch at about 20. When dry they are usually more 

 divergent, and in any case there is considerable variation, but 

 most of the young branches are as described. When older they 

 tend to diverge more, and the thicker branches are apt to be very 

 irregular, partly by the process of development, and often no 

 doubt through some of the branches being lost. A very note- 

 worthy character is the reversal of the aspect of the young 

 branches, so that their hydrocladia have the front facing the 

 front of the parent branch, hence the polypidom has not a dis- 

 tinct anterior and posterior aspect, like A. tasmanica and 

 A. billardi, in which the branches all face in the same direction. 

 The peculiar mode of branching in the present species results in 

 the young branches coming between the branch from which they 

 spring and the penultimate branch, it is easily understood 

 therefore how through the repetition of this process the ramifica- 

 tion will become very dense. In some cases a very small branch 

 is found springing from a part of an old thick branch otherwise 

 bare, apparently a new growth ; the inference would be that such 

 branches must spring from the supplementary tubes by which 

 the primary stem is enclosed, but I have not been able to verify 

 this. The hydrocladia reach a length of about three-quarters of 

 an inch. As in the allied forms the branches commence with a 

 series of internodes (about half a dozen) bearing only sarcothecaa. 



The minute structure indicates a distinct relationship with the 

 A. crucialis group, notwithstanding the total difference in habit. 



