5 
the attempt to work upon these lines that there can be any hope of reducing the present chaos 
of our system. In this connexion, reference may be made to a character of great interest. 
In several genera the main stem is tubular in form instead of being solid, a character 
which is sometimes spoken of as fistulose. We find such a condition in Stylaster amphiheloides, 
Errina labiata, Conopora tenuis, and it is obviously comparable with the condition in the 
Zoantharian forms Neohelia'), Amphthelia and others and in the Alcyonarian genus So/enocaulon. 
In many cases it is found that the cavity of the stem contains an Annelid worm (Nereds sp.°) 
or a Crustacean (A/fheus). It is improbable that the epizoite actively hollows out the stem. 
It is more probable that the stem of the young colony grows round and encloses the epizoite 
in the manner of a coral gall. In any case, however, the fistulose character of the stem cannot 
be regarded as a useful one for generic or even specific distinction. 
In the following description of specimens and species certain measurements are given 
indicative of the size and form of the colony. It is necessary to explain the method and 
terminology of these measurements. 
The exact size of the colony can only in a few rare cases be determined. Very few 
specimens that were obtained are perfect. They are nearly always more or less broken by natural 
forces in situ, by the dredge, or in transit to the systematist. Sometimes the injury is slight, 
and the measurements can be estimated with considerable accuracy, but frequently the specimens 
are broken into many fragments and in such cases the measurements can only be guessed to 
be within certain wide limits. 
We have endeavoured in all cases to estimate the greatest distance from the base of 
attachment to the tip of the most distant branch taken in a line approximately perpendicular 
to the base of attachment and this we have termed the height of the colony. We have also 
estimated the width of the colony by the measurement of the line at right angles to the line 
of height stretching between the apices of branches at the greatest distance apart. We have 
also measured the diameter of the stem at a point just above the disc of attachment and as a 
guide to one feature of the ramification the diameter of the main stem at a point quite close 
to the attachment of the primary branch. 
In a very large number of Stylasterids the method of branching is flabellate, that is to 
say the branches arise in one plane and give the colony a general fan-like shape. In some of 
these the cyclosystems are all or nearly all situated on one side of the flabellum, possibly it is 
on the side facing the direction of the prevailing current that brings them food. Whatever the 
cause may be however, it is useful to employ a term to designate the surface on which the 
cyclosystems occur and that on which they are generally absent. The former therefore we call 
the ‘anterior’ surface and the latter the “posterior” surface. In like manner the surfaces of 
each branch, which are in the same plane as the plane of the flabellum, are called “anterior 
and posterior sides” respectively. The other surfaces are called the “lateral sides’’. 
The terms used in the descriptions of corals are unfortunately not uniform and a general 
revision of them is necessary. In the present memoir, we use the word Hydrophytum to signify 
1) E. M. Pratt. WILLEY’s Zoological Results, Pl. V. 
