REPORT ON THE HYDROIDA. 
33 
ceasing to be covered by the peripheral tubes towards the distal parts of the colony. 
Hydrothecse tubiform, with entire margin, destitute of operculum, sessile or pedunculate, 
with their walls never adnate to the hydrocaulus, and with the cavity uninterruptedly 
continued into that of the peduncles or of the parts of the stem from which they directly 
spring. Hydranths with a conical hypostome. 
Gonosome not known. 
The genus Lafo'ea was founded by Lamouroux in 1821, and since then has been 
more exactly defined by Sars, and further limited by Hincks. Our increased knowledge 
of the species, however, and the detection of the perisiphonic nature of the fascicled 
stem, render necessary a still further amendment of the definition, and the diagnosis 
here given will, I believe, mark out the true limits of the genus. 
The most important characters of this diagnosis will be found in the perisiphonic 
fasciculation of the stem, the complete freedom of the hydrotheca walls from the 
hydrocaulus, and the uninterrupted continuity of the cavity of the hydrotheca with that 
of the peduncle, or, where no peduncle is present, with that of the axial tube from which 
it springs. By this last character among others it is distinguished from such forms 
as Campanularia, in which the cavity of the hydrotheca is differentiated from that of 
the supporting peduncle by a basal constriction, forming a more or less pronounced 
perforated diaphragm. 
The distal parts of the colony are always free from the peripheral tubes, a character 
which Lafo'ea possesses in common with Cryptolaria. In Lafo'ea the hydrothecse are 
never adnate to the axial tubes in any part of the colony ; in Cryptolaria they are 
so adnate where the axial tube ceases to be covered by the peripheral. 
It is a remarkable fact that, notwithstanding the great abundance of some of the 
species, no trace of the gonosome has as yet been detected in any true Lafo'ea. 
Hincks has united under Lafo'ea, a number of minute Gampanularian Hydroids which 
the definition here given will exclude, not only on account of their non-fascicled stem, 
but of the distinct differentiation of the cavities of their pedunculated hydrothecse. 
Though we know T nothing of their gonosome, w T hile our knowledge of them is in other 
respects also imperfect, we shall I believe be justified in uniting these little cup-bearing 
species under a separate genus, to which I have assigned the name of Hebella. Their 
separation from Campanularia (as limited above, p. 18) may possibly appear arbitrary, 
but the more cylindrical cup-shaped form of their hydrothecse contrasts with the 
campanulate form of Campanularia, and in our very imperfect knowledge of the species 
will justify the provisional allocation here suggested. 
A form with tubiform hydrothecse but with creeping non-fascicled stem is regarded 
by Hincks as a variety of Lafo'ea dumosa, Fleming. I am unable to accept this view, 
for I regard the perisiphonic stem as an essential character of every true Lafo'ea. I have 
accordingly united in a separate genus the monosiphonic Campanularians with tubiform 
(zool. chall. exp. — part lxx. — 1888.) Aaaa 5 
