410 Dr. F. Miiller on a Hybrid Balanus. 
in the middle between the carina and the rostrum; the seuta 
are always, considerably narrower; the rows of pits on the 
outer surface are never wanting; nor on the inner surface are 
adductor ridges, traceable nearly to the basal margin, to be 
seen; the terga never have such narrow spurs, or a longitu- 
dinal furrow, or ridges for the muse. depressor projecting be- 
yond the basal margin ; the strong curved teeth on the cirri of 
the third pair and the strong tooth on the peduncle of the fifth 
pair are never wanting; there are never more than four pairs 
of setee on the posterior cirri, &e. 
In B. assimilis, on the contrary (a species so common here 
that every potsherd, shoe-sole, or rope’s-end which has lain 
for some time in the sea is covered with it), I have never seen 
a similar reddish colour to that presented by one of the sup- 
posed hybrids; I always found the radii he narrow, covered 
with a thin membrane, never broad and shining; I always 
found short spines between the hairs of the opercular pieces, 
and the spur narrower, the labrum always beset with nume- 
rous teeth; and in the animals which I have to-day examined 
for this purpose, but which, indeed, are not very numerous, I 
found constantly six pairs of setes upon some joints of the 
posterior cirri, not to mention other small distinctions. 
It is evident that the differences from either species are too 
considerable for a mere stents they would be of sufficient 
importance to lead us to regard- our animal as a distinct spe- 
cies, if there were not other considerations opposed to this 
view. Species of Balani, where once they occur, do not usu- 
ally appear so isolatedly that in the course of a month only 
four specimens can be brought together*. And how surprising 
would it be that upon the stem of Carijoa a third species 
should be domiciled amongst B. armatus and assimilis, stand- 
ing in so peculiar a manner in the middle between the two 
species as do our animals, which agree with B. armatus in 
almost everything by which they differ from B. assimilis (in 
the coloration of one of the shells, in the firm union of their 
pieces, in the structure of the shining striated radii, in the 
structure of the labrum), and which in almost everything by 
which they differ from B. armatus (in the formation of the 
walls, the aperture, the opercular pieces, &c.) agree with B. 
assimilis, and, again, in other respects (as in the number of 
* IT cannot say exactly among what number of B. armatus the four 
hybrids were found, as I have used up a great quantity of the former 
without counting them; the number may be about 400. For a month or 
more I haye daily dived upon the Carijoa rock whenever the sea was 
sufficiently quiet, and not unfrequently obtained from thirty to forty 
Balani at once upon the polypes. brought. up. . 
