Australian Hi/drouls. 137 



Hab. — Fiji, on a coral: off Cimiheihuid Ids.. 27 fathoms 

 (Busk): Torres Strait (Haddon) : on the re.-f at Hulule. MaU- Atoll 

 (BorradaileV 



Busk's original description of F. hrevirostris was insufficient to 

 admit of its identification, but Dr. Kirkpatrick kindly compared 

 one of my specimens with Busk's type, and has also sent me a 

 specimen from Haddon's Torres Strait collection, which proves 

 similar in all respects to my own specimens from Fiji. These I 

 ■described in 1881 under tlie pi-oposed name of A. het trocar pa, but 

 I afterwards referred them to the A. ritiuua of Kirchenpauer 

 (" Catalogue," p. 152). The later descriptions by Billard of both 

 A. vitiana and A. hreviroslris seem to prove, however, that this 

 reference was erroneous. 



Nevertheless, the two species have many points of agreement. 

 Both were found growing on a coral from Fiji; in size, habit, and 

 colour they agree closely, as well as in some minor particulars. The 

 branches in each species spring from the supplementary tubes, so 

 that branching cannot occur till the polysiphonic structure is 

 developed, which in many cases is not till growth is well advanced. 

 One of my specimens of A. Jirevirofttris consists of a single shoot 

 bearing five corbulae, but with no trace of fasciculation. The proxi- 

 mal part of the stem is naked at first, then supporting a few large 

 sarcothecae in a single row before the hydrocladia are reached. 



The principal distinction l)etweeH the hydrothecae of the two 

 species is that in A. vitiana there is an anterior intrathecal ridge 

 similar to that of Lytocarpus phillipiiiuf:, while in A. brevirosfris 

 the distal part of the hydrotheca,. though ul)ruptly recurved, does 

 not become united to the proximal portion, so that instead of an 

 intrathecal ridge there is on the apocauline side of the hydrotheca a 

 deep constriction. In A. vitiana the two principal teeth on each 

 side of the hydrotheca are said to be l)ifid. and the internode is 

 described as having three septal ridges, or sometimes only two. 

 A. brevirosfris has the lateral teeth simply triangular, and there 

 is scarcely ever more than one septal ridge, which subtends the 

 inthrathecal fold. In A. vitiana the internodes are stouter, as is 

 the mesial sarcotheca, and the canaliculate condition of the latter is 

 more apparent. 



Both Billard's and Borradaile's figures show the constriction of 

 the hvdrotheca as much less abrupt than is usuallv the case. In 

 Haddon's specimen, as well as in my own. such hydrothecae are 

 abundant, but in both cases the majority are of the more abruptly 

 bent type. 



