46 AMPHIOTBNE AURICOMA.
the smallest yet observed, but its disposition is similar, for it has a slight ventral fold on
each side to aid in guarding the tentacles. The anterior or free edge is fringed with
comparatively long subulate fimbrias. The tentacles are perhaps less numerous than in
allied forms, but their structure is the same, the distal ends being often flattened and with
a median groove joining that proceeding along the column.
The folds at the sides of and behind the mouth in the main agree with those of other
species.
The second cirrus or tentacle arises on the dorsal edge of a glandular ridge, which
ventralward presents two divisions, viz., an outer transversely elongated rounded
eminence, and a larger inner ridge which passes with slight obliquity to a median
division. In front of this prominent ridge are two or three minor ones, the grooves
of which öonverge toward the mouth. From the dorsal edge of the cirrus a small
ridge runs dorsally, but soon disappears behind the fimbriated rim of the scabrous
region.
The branchiae occupy a similar position to those of Lagis Koreni, but are specially
modified in so far as the lamellae of the first branchia are proportionally larger, both
broader and longer, and the basal axis to which they are attached is shorter. Thus the
apparatus is more fan-shaped and less like the scorpioidal cyme. As in Lagis the larger
lamellae are internal, and they gradually diminish to the small external end. The second
branchia is considerably less in all its parts, but it has the same abbreviation of the basal
axis or stem. The first branchia would appear to belong to the segment behind the
second long cirrus, and which sends a prominent glandular ridge to the mid-ventral line.
The second pertains to the ridge immediately behind, and which also passes to the mid-
ventral line, where, as in the previous form, a separate shield occurs. It is further
distinguished by a considerable, flattened, glandular lobe immediately following the
branchia, which would apparently act as a guard to the first branchia. So far as
these parts show, three segments would thus seem to pertain to the collar-region, viz.,
that of the second long cirrus and the two branchial segments.
Thé next region of the body consists of three bristled segments devoid of hooks as
in allied forms. The appearance of these, however, suggests a sub-division, for the
two anterior have the thick glandular ridges, the first with a single central division and
the second with two central divisions, whereas the third has only a long, slender, non-
glandular ridge as in those which follow. The region appears to be on the whole considerably
foreshortened in contrast with Lagis. The first two bristle-tufts are very small,
and they arise from the non-glandnlar or dorsal part of the ridge. The third is considerably
larger, and is usually closely applied to the surface of the dorso-lateral region.
Each tuft has the stout, tapering simple bristles with traces of wings distally below the
tapered point, and all have, in addition, a few in which the spear-like dilatation at the
tip is present, with the hair-like point and serrated edge. All these bristles have a
peculiar ring-like dilatation at the base.
The third region is characterised by the great development of the lateral lamellse
for the hooks, as well as for the long and strong bristles at the dorsal edge. All the
latter are very powerful anteriorly, dilating from the base upward until full diameter is
attained, and then tapering to a delicate hair-like tip (Plate CXXIV, fig. 2 a). Besides
these are the bristles with the spear-shaped enlargement and the finely-tapered tips,
the shafts being also robust. The posterior bristles are considerably smaller, but
they keep to the same type, those with the spear-shaped tips being proportionally
longer.
The caudal hooks are situated on each side of a small keel (notched at its free end)
which marks the median dorsal region of the caudal appendage. They are distinguished
by their comparatively great length and straightness, by the rapid diminution at the
neck, and by the abrupt curve and sharp condition of the hook at the tip (Plate CXXIV,
fig. 2 b). The edge of the process is deeply and symmetrically notched, usually curved
ventrally, and the dorsal lip of the vent is prolonged as a somewhat flattened conical
process with a dorsal papilla on its surface which curves beyond the split ventral lip.
The dorsal surface of the process is concave, forming a deep groove, whilst the ventral
is convex and grooved by oblique furrows, directed outward and backward. It seems to
be easily regenerated, even before the bristled segments necessary to complete the series
are' formed, and thus some examples are peculiarly short and broad, the tapered posterior
region of the body not yet having been reproduced, whilst the caudal process is fully
developed.
The lamellar hooks (Plate CXXIV, fig. 2 c) have six teeth from the crown downward
; then follows a finely spinous process (like a large tooth with serrations), below
which is a notch directed upward, and lastly the rounded prow which is nearly in a line
with the face of the hook. The shaft is short and comparatively broad. The finely
serrated part above the prow is slightly longer proportionally than in Pectinaria belgica,
but in some' positions the same double contour of the tip of the prow is visible.
The tube (Plate CXVIII, figs. 5—5 b) is gently curved and finely tapered, especially
in the smaller specimens, and composed of finer sand-grains than in Lagis Koreni, neatly
cemented together, the tubes of young forms especially having very minute grains, and
in any case the tubes are perfectly rounded and apparently smooth, for the slight
elevations caused by the sand-grains are only visible under a lens, and a certain amount
of translucency is present, for the quartzose sand-particles are each fixed in its setting
like a jewel, so that there is little interference with the light. Moreover, the tube has
only the thickness of such grains, with a delicate coat of the secretion internally. The
smaller end of the tube has grains considerably finer than the wider, but they blend into
each other so insensibly that it is only by comparing the distant parts that the difference
is observed. Like many others the annelid works at its tube only during the night.
In the “ Porcupine” Expedition of 1869 empty tubes occurred in deep-sea mud in which
no sand-grains were present, the only convenient hard particles being fragments of the
siliceous spicules of sponges, the animal constructing its tubes of these with the utmost
neatness and regularity in horizontal rows from end to end, somewhat after the manner
of close basket-work (Plate CXVIII, fig. 5 a). The fragments are short, and conduce to
the perfect rotundity of the tube, which only presents the slight convexity of each spicule
at the edge, the outline being minutely crenate under the microscope. The cement
fixing the spicule is in small quantity, just sufficient to render the tube strong without
interfering with its transparency and smoothness. The workmanship of these tubes,
indeed, excites admiration, no less for the skill and perseverance of the architect than