THE ANNALS 
MAGAZINE OF NATURAL HISTORY. 
' [FOURTH SERIES.] 
No. 6. JUNE 1868. 
<i 
<I 
XLVIU.—On Balanus armatus, and a Hybrid between this 
Species and Balanus improvisus, var. assumilis, Darw. By. 
Dr. Fritz MGLLER*, : 
[Plate XX.] 
In Acasta purpurata, which lives in the bark of an Isis, as 
also in Acasta cyathus and sulcata, which live in sponges, 
Darwin found that, in the outer branch of the fourth pair of 
cirri, the anterior margins of some of the inferior pee were 
armed with strong decurved teeth, by which means, he thought, 
these joints were converted into jaw-like structures, and became 
wonderfully well fitted to seize any prey (Darwin, ‘ Balanide,’ 
p- 84 & 311). Inno other Cirripede has a similar armature’ 
n hitherto detected. | 
_ When I first met with Balanide imbedded in a sponge, I 
of course at once looked for this armature, and had the grati- 
fication of finding both branches of one of the cirri equipped 
with similar but much more numerous teeth. But on elas 
examination it appeared, to my great astonishment, that in 
my species it was not the fourth, but the third pair that bore 
the teeth, and that the animal was not an Acasta, but a true 
Balanus with porous walls and a porous base, and scarcely 
distinguishable, as regarded its shell, from Balanus trigonus, 
Darwin. : 
Occurrence.—This Balanus armatus (as I have called it, on 
account of the abundant armature of its cirri) lives almost ex- 
clusively in sponges. I found the first three mutually adhe- 
rent shells (two of them with the animal still in them) thrown 
up upon the shore, and rather worn. They appeared not to 
have been attached to a solid body; and in sheltered parts, 
especially beneath the deeply excavated base of one specimen, 
there was some loose sponge-mass, which, from the spicules, 
* Translated by W. S. Dallas, F.L.S. &c., from Wiegmann’s ‘ Archiv,’ 
1867, pp. 329-356. 
Ann. & Mag. N. Hist. Ser. 4. Voll. i. 28 
