HYDIUJIDA. BALE. OO 



what shorter and less everted in II. intermedia than in the 

 other species, and the border is not quite so low at the sides, In 

 all three species the tirst hydrotheca on each hydrocladium differs 

 from the rest in having the aperture quite horizontal, and the 

 lateral teeth nearly obsolete, one generally more so than the 

 other. 



Each species has its own characteristic condition of the axils 

 at the bifurcations. In H, furcata each axil is generally 

 occupied by a hydrocladium of one iuternode, the hydrotheca on 

 which is without a mesial sarcotheca. This hydrocladium 

 springs from the back of the axil ; the usual cauliue sarcothecas 

 in front are wanting, but there is a pair at the back, seated one 

 on each side of the base of the hydrocladium, and facing out- 

 wards. Of H. intermedia I examined a number of specimens, 

 but in none were these short hydrocladia present ; there are 

 however, in all cases a pair of divergent cauline sarcothecse 

 behind the axil, approximate at the base or completely united 

 and confluent, but in either case communicating with the interior 

 of the hydrocaalus by a single large orifice. H. baileyi has 

 behind the axil in the only specimen available for examination a 

 pair of sarcotheca? close together at the base, narrower than in 

 //. intermedia and directed more upward ; it has also a 

 sarcotheca in front below the axil, and below this a perforation 

 with a fragmentary border, probably also a more rudimentary 

 sarcotheca. 



The most salient feature which distinguishes H. intermedia 

 from its nearest ally, H. furcata, is its large size and robust 

 habit, with its long hydrocladia, reaching about 18 mm. in 

 length (those of H. furcata being much shorter). In the 

 minute structure of H. intermedia the greater length of the 

 hydrothecal iuternodes, and the consequent less crowded condition 

 of the hydrothecee, furnish the most striking distinction. The 

 internodes average about '41 mm., and those of H. furcuhi 

 about *81. The difference is not so much in the hydrotheca 1 as 

 in the internodes, accordingly it will be observed that in a front 

 view the hydrothecae of II '. furcata are closer together, the 

 proximal ends of the hydrotheca; being just over the nodes, while 

 in H. Intermedia there is an intervening space. I have not 

 seen in H. furcata the noticeable narrowing of the hydrothecre 

 and their iuternodes, which in H. intermedia occurs towards the 

 cuds of the hydrocladia, and the hydrotheca of the latter species 

 do not so completely face the anterior side of the polypidom. 



The colony of H. >>/tcrint>dia consisted of a good many shoots, 

 and among the specimens which T examined I did not observe 



