330 MR. A. HANCOCK ON A BURROWING BARNACLE 
the upper surface is flat, and has in the centre a broadly ovate, 
horny plate, most distinct in old individuals, but never entirely 
covering the part, the margins always extending beyond it. This 
plate is of a reddish horn-colour, and is generally furnished with 
a few indistinct radiating ridges and tubercles, corresponding to 
the radiating lines and punctures seen on the surface of the matrix. 
The animal, as before stated, lies immediately below the sur- 
face of the matrix, and is entirely free, except at a point just 
behind the slit, and in front of the horny plate, where there is a 
strong muscular attachment to the upper wall of the chamber. 
The longitudinal opening of the animal, corresponds to the slit 
on the surface of the matrix: this opening is kept pretty accu- 
rately plugged by the thickened valvular lips of the animal, ex- 
cept when it is in watch for its prey, at which time a slight 
opening in front permits the passage of the prehensile arms. 
These occupy the same position within the head or neck, as they 
do in the valvular part of the pedunculate Cirripedes, being 
placed immediately in front of the mouth. They differ however 
considerably from those of all other Cirripedes. The arms of this 
animal are only six in number; they are short and set ina circle 
on the extremity of a soft, fleshy, cylindrical pedicle, which is 
undoubtedly a prolongation of the true body of the animal ; the 
circle opens a little behind, in the direction of the mouth. The 
arms are each composed of three articulations, the first or lowest 
being much the longest, the last the shortest ; they are all fur- 
nished with a few hairs on the margins and extremities: the four 
arms next the mouth, have attached to their inner margins at the 
junction of the first and second articulations, an oval cushion- 
like body placed longitudinally, and wrinkled transversely, most 
probably for the purpose of prehension. Immediately behind the 
arms, projects a large conical body, containing the mouth, which 
is placed near the base in front towards the circle of arms. The 
greater portion of this body is composed of the upper lip, which 
differs considerably from that of the other Cirripedes. In this it 
is delicate and horny, being enormously developed and sur- 
mounted by a sort of rostrum, which projects upwards and for- 
wards, and terminates in a slightly produced obtuse point ; the 
