14 
THE VOYAGE OF H.M.S. CHALLENGER. 
of the hydrophores, pyriform, with a lateral tubular orifice and rounded summit, or with 
the summit broadly truncate, regularly and distinctly annulated throughout. 
Locality. — Simon’s Bay, Cape of Good Hope ; shallow water. 
Halecium dichotomum is a very distinct and remarkable species. The beautifully 
annulated condition of the gonangia presents a character not elsewhere met with in 
Halecium. In the general architecture of the hydrocaulus, and in the plexus of tubes 
with which the proximal ends of the stems are continuous, Halecium dichotomum closely 
approximates to Halecium cymiforme (PI. VII.), but presents a combination of characters 
which separate it by a wide interval from every other known species of Halecium. 
The stems, which rise free from the basal plexus to a height of from about half an 
inch to an inch, consist of a series of cylindrical tubes, each tube springing from a point 
close to the distal end of that which precedes it. These tubes represent the internodes 
of the stem, but instead of being as in other cases directly continuous with one another, 
they have their distal ends free. Each of these ends either directly supports a hydranth 
— the entire internode thus representing the basal segment of a hydrophore — or is 
continued by one or more superimposed segments. The stem may thus be regarded as 
a series of long, nearly straight, cylindrical hydrophores, either simple or extended by 
the superposition of accessory segments, each hydrophore springing, one from the other, 
so close to the distal end of that which precedes it, and at so high an angle, as to form 
a geniculate linear series. The long cylindrical internodes which in this way make up 
the stem are often prolonged by two instead of a single internode, both springing 
opposite to one another from points close to the distal end. Two branches which exactly 
repeat that from which they spring are thus formed, and give the dichotomous character 
to the ramification of the colony. 
The basal plexus consists of an entangled mass of tubes whose branches unite freely 
with one another. These tubes, though their diameter is scarcely less than that of the 
stem, do not present the regular succession of internodes met with in the latter. Their 
walls are marked by rather irregular annular rugae. They give off hydrophores which 
spring here and there from their sides, and some of these as in the hydrophores of the 
stem support laterally situated gonangia. 
The fascicled condition of the stem found in most species of Halecium is usually 
but slightly marked in Halecium dichotomum , though some of the old stems may become 
very much branched and fascicled. The fasciculation, however, is in most cases chiefly 
confined to the basal plexus, where two or three tubes may here and there be seen united 
by their sides to one another. 
The gonangia present a slight difference in form. While the greater number have 
the summit rounded and arched over the lateral orifice, this part is in others broadly 
truncate. The difference is probably dependent on different degrees of maturity ; at all 
