Dr. F. Miller on a Hybrid Balanus. 409 
similis; as in the latter species more than half the upper 
margin was clothed with hair. 
irrt.—First pair: the longer, 19-22-jointed branch was 
in three animals about twice as long as the shorter one, in the 
fourth about one-fourth longer; the shorter branch in two 
animals had fourteen joints (in the others eleven and thirteen). 
I have not met with so great a number of joints in B.armatus; 
in B. assimilis it is frequently still greater (fifteen to eighteen). 
In the latter species, as is well known, the two branches are 
generally of almost equal length; nevertheless, even in this, I 
| — observed a difference of nine joints (fifteen and twenty- 
our). mn 
_ Second pair: thirteen to sixteen joints in the outer, twelve 
to thirteen in the inner branch; in B. armatus, eleven to thir- 
teen in the former, nine to ten in the latter; in a B. assimilis 
which I have at hand I count seventeen and sixteen. 
Third pair: in three animals I found in the outer branch 
thirteen to sixteen, in the inner twelve to fourteen joints ; the 
fourth had on one side thirteen and twelve, and on the other 
twenty-one and twenty joints! The bristling and armature 
of this pair of feet were in all four animals the same as in B, 
assimilis ; the sete: on the inner surface of the joints were very 
numerous; and on the outside there were only straight spines 
and points, chiefly directed upwards. 
Fourth to sixth pairs: the flexural side of the upper joints 
in the fifth and sixth pairs of cirri in all four, and in the 
fourth in three animals, bore five pairs of sete; the fourth 
animal had only four pairs of sete on the joints of the fourth 
pair of feet. In B. assimilis six is the usual number of pairs 
of setze on the joints of the posterior cirri. ‘The outer surface 
of the joints in the fourth was armed in the same way as in the 
third. No trace of the strong tooth which in B. armatus stands 
on the peduncle of the fifth pair was to be found in any of the 
four animals. 
Penis as in B. armatus. In B. assimilis this organ is ge- 
nerally beset with longer and more numerous hairs. 
Affinities —The discovery just described seems to me to 
admit no other supposition than that the four animals. are 
really hybrids of B. armatus and B. assimilis. If we do not 
choose to let them pass as such, we must either regard them 
as a variety of B. armatus or of B. assimilis, or as a distinct 
species. 
But in B. armatus the walls never have translucent longi- 
 dinal lines, or transverse septa in the tubes which run through 
them ; the greatest breadth of the aperture never falls deatie 
Ann. & Mag. N. Hist. Ser. 4. Vol.i. 29 
