178 
THE VOYAGE OE H.M.S. CHALLENGER. 
in one or two instances I have noticed, instead of the ovoid, probably embryonic mass, 
the remains of a polypide with tentacles and digestive organs like those of the inhabitants 
of the zooecial cells, whence we may suppose that the embryonic mass is developed from 
or in a polypide, which is gradually replaced by it. 
3. The presence of a median pore or its equivalent, which though not formed or 
developed in the same way in all the Adeonese, doubtless subserves the same function in 
all, and in every case appears to me to differ widely in nature from the lunate pore in 
Onchopora, Microporella, &c., as well as from the tubular pores in Tessaradoma, Tubu- 
cellaria, &c. 
In the Adeonese, the pore seems to be formed in at least three distinct ways. The 
most common perhaps is by the constriction off of the lower part of the orifice, which in 
such cases is more or less deeply emarginate or sinuated. But sometimes it appears to 
arise from an arrest of calcification of the front, independently of the orifice altogether, 
whilst in other cases it is represented by what may be termed a “ perforated area,” that 
is to say, a depressed area or space, the bottom of which, formed by a thin calcified 
lamina, is pierced by from one to six or eight small circular fimbriated porules, the 
whole bearing some resemblance, if not some homological relation, to an interzooecial plate, 
or so termed “ Rosettenplatte.” Besides this pore the front of the zooecial cells and 
sometimes of the ooecial also, is furnished with one or more sessile avicularia. 
4. In several species, if not in all, besides the ooecial and zooecial cells, others may be 
seen, usually on the extreme border of the lobes, branches or fenestrse, though sometimes 
interspersed, which may be termed avicularian cells, that is to say, which are wholly 
converted into “ vicarious ” avicularia, whose large mandibles often afford very useful specific 
characters. 
5. To these more important characters may be added one which though minute is so 
constant as to deserve especial notice. It consists in the circumstance that in the entire 
group the avicularian mandibles both large and small always exhibit a projecting point 
or articular process at each end of the base, into or close to which the erector muscles 
are attached. To which may be added that so far as I have noticed the occlusor muscle 
of the mandible is always single instead of consisting of two bands as usual. 
In doubtful fragments the above character of the mandibles will alone often 
be found useful as an indication of the affinities of the species. 
Though the division is to a certain extent arbitrary, I propose to divide the Famil} 7 
into two or three groups, which may provisionally at any rate be regarded as of generic 
value. 
These are : — 
1. Adeona, Lamouroux. 
2. Adeonella, n. gen. 
3. Reptadeonella, n. gen. 
