REPOET ON THE ANNELIDA. 
129 
A short and somewhat elliptical as well as massive though pale and soft form, 
distinguished by its large smooth scales, short tentacle and pal]3i, the great size and 
paucity of the ventral bristles (not more than two being present in any case), and the 
absence of the dorsal bristles. It measures, including the protruded proboscis, about 
1 8 mm. in length, and is 1 1 mm. transversely from tip to tip of the bristles. 
The head (PI. XV. fig. 3) is wider than long, and furnished with four large eyes, the 
smaller pair lying at the posterior border, and nearer each other than the anterior pair, 
which occupy the lateral prominence about the middle of the head. The latter are large 
oval eyes, having a whitish opacity in the centre, as also have the posterior pair. A well- 
marked median hollow separates the broad head into two halves. The base of the 
small subulate tentacle proceeds from the anterior margin of the head, and after an 
interval on each side is the antenna, the base of which is slightly longer than that of the 
former, while the process itself is somewhat shorter. The small palpi lie exterior to the 
latter and inferiorly, and the tips do not reach so far outward. They are short,, smooth, 
nearly cylindrical, except at the blunt conical extremities, which have a few brownish 
pigment-grains just above the distal narrowing. They are the smallest palpi yet 
observed, and with other points indicate a change of type. The tentacular and dorsal 
cirri are simple, smooth, filiform processes. The latter in the middle of the body 
scarcely reach beyond the fleshy part of the foot, but as usual are a little longer in front 
and posteriorly. Their bases are greatly enlarged, forming tumid masses, from which 
the somewhat slender cirri proceed (PI. XV. fig. 3). The ventral cirri are short and 
subulate, and do not reach the bases of the bristles Ijy a long interval. The ventral 
})apilla is moderately developed, and is normal in position. 
The proboscis (PL XVI. fig. 4) shows the typical nine papillae dorsally and ventrally, 
and the jaws are amber-coloured, slender, and sharp. Two elongated papillae occur on 
each side, about the middle of the extruded region. 
In transverse section the posterior region of the proboscis follows the dermal tissues 
in diverging from that of the ordinary forms of the Polynoidae. Externally is a well- 
marked stratum of circular fibres, beneath which the chief layer occurs, viz., that 
apparently homologous with the hypodermic coat, and consisting of a thick glandular 
investment, the folds of which often have a pennate appearance in section jDrecisely as in 
the anterior region of the Nemertean proboscis. The basal part of the coat is the more 
fibrous, the distal the more glandular. 
If this layer correspond to the great muscular coat of the ordinary type, then 
the further differentiation of the fibrous basal region into the latter layer, and the con- 
densation and differentiation of the distal into the firm stripe of hypoderm and the 
dense cuticle occurs. Perhaps, howmver, the dense layer is an addition. No other 
layer is present. The organ differs from the ordinary type in simplicity, and thus 
corresponds with the condition of the skin and the bristles. In any case, the 
(zOOh. CHALL. EXP. — PART XXXIV. — 1885.) LI 17 
