The second pair arë elongated transversely as in the other form, but are distinguished
by the great .length of the cilia on the outer border. A few cilia also occur
along the posterior edge.
The succeeding scales. in the anterior third do not differ much in shape from those
of P. minuta, but the cilia are much longer and stand stiffly out. They occur on the
external margin and the outer half of the posterior edge. They are less numerous than
in the large examples of the typical form, but agree with the smaller in this respects.
The posterior scales have about the same number of cilia, but they stand stiffly out
like rays.
This form is .distinguished from the preceding in spirit by an olive spot on the scale,
with a pale centre at the scar for attachment. Occasionally, as in an example of this
variety from Lochmaddy, the cilia on the scales are fewer and longer, being filiform
tapering processes without the terminal enlargement.
In both varieties the areolae, especially towards the inner edge, are well marked.
Feet.—The second foot is bifid, with two well-developed spines. The dorsal lobe
forms a rounded eminence with a smooth surface. The bristles are comparatively short,
slender, and taper to a very fine hair-like tip, minutely spinous. The inner forms taper
more abruptly than the outer, and the tips are often bent nearly at right angles to the
base. The ventral lobe is longer than the former, bluntly conical, and with numerous
small papillas on its surface. The ventral bristles have stout shafts dilated at the. tip,
and with numerous rows of spines on the convex margin, thus differing from those of
the arctic examples (P. minuta, Fabr., typical), which have féw. The distal region
forms an elongated process-'—hooked at the tip, and with a series of spikes along the
ventral edge. The tip in the arctic forms is more robust and proportionally shorter.
In the typical foot (Plate XXXI, fig. 14) the dorsal lobe presents a prominent
process and a broad, slightly convex margin externally for the bristles, the spine
piercing the apex of thé convexity. The bristles (Plate XLII, fig. 23) form a dense
tuft, directed outwards and downwards, and are slender and tapering, with well-marked
spinous rows.
The ventral lobe has the shape of an oblique cone, with the spine issuing from the
apex and with numerous papillae over the surface. The shafts of the bristles (Plate XLII,
fig. 24) are somewhat shorter and stouter than in the northern form (P. minuta, typical),
and the convex edge óf the tip has more numerous spikes. . The falcate tip is shorter,
more curved (the hook more pronounced), and the spines along the edge are often absent.
Indications of these, however, are seen..
Posteriorly, the dorsal bristles have finer spikes, and the ventral have fewer rows of
spines at the convex distal region of the shaft, while the terminal portion is more
slender and proportionally longer. The papillae on the ventral division are fewer and
somewhat longer. The ventral cirrus is short and tapered.
In examples from Lochmaddy only three or four spikes occur on the distal end of
the shafts of the ventral bristles. Some from Bressay Sound show more numerous
though finer spikes at the distal end of the shafts, as in those from St. Andrews. In a
small one from St. Magnus Bay they were too indistinct for determination, though
they appeared to be smooth. In a small example from Herm no spikes were present
on the distal pieces of the ventral bristles. In specimens from the St. Lawrence,
Canada, the bristles agreed more with the arctic forms, and one had a translucent
granular deposit on them. The spikes at the end of the shaft were indistinct, but this
also occasionally occurs in the British examples.
In considering the two varieties (inornata and eximia) it is clear that no reliable
distinction can be drawn from the structure of the bristles, and this is probably more
important than the condition of the cilia on the scales. I t is true the end of the shaft is
most spinous—that is, has a longer series of spines from above downwards—in var.
inornata, and that the dorsal bristles are more distinctly spinous, and the ventral warts
or papillae more conspicuous, but the characters are not new, and only vary in degree,
and are probably due to the surroundings, with which we are, perhaps, not fully
acquainted. The steps from var. eximia to var. inornata, and thence to the typical
rmnuta from the arctic seas, are easy, both as regards scales and bristles.
After a careful consideration of all the facts it has been thought best to unite the
varieties into a single species.
Reproduction.—Male elements as minute granules occurred in August at Lochmaddy.
At St. Andrews ripe males are common at the end of June, so that the breeding period
would seem to be in July. The spermatozoa have globular heads and long tails, and
resemble those of Lepidonotus squamatus, a species with the same breeding period. The
examples of P. minuta from Greenland present ova in July.
Development.—Trochospheres, apparently of this species, occur near the bottom on
September 12th, presenting only four crenations posteriorly to indicate the segments.
On September 10th the youngest stage has a bluntly conical prostomial region,
which appears to occupy about half the bulk of the animal. Two small black specks
are situated posteriorly. At each side are the short tentacular cirri. Four bristled feet
follow, with stout bristles having the typical structure. Two spines occur on the dilated
end of the shaft, the most prominent being inferior. Besides these stout bristles, each
foot has one or two much more slender forms, with a long, tapering, diaphanous terminal
piece, evidently a larval ventral bristle. The dorsal bristles have the adult structure,
being slender, tapering, hair-like, serrated bristles. The dorsal cirrus is much enlarged
at the base, but with a slightly tapered tip.
What appear to be three pairs of scales have the aspect of globular organs on a
pedicle, each with several large truncate papilla© projecting from the edge. These
papillse are out of all proportion to the condition in the adult. Viewed from below the
ventral cirrus shows a basal swollen region (ceratophore) and a two-jointed cirrus, while
some distance inwards is a globular papilla. The body, which is marked by transverse
lines at this stage, terminates posteriorly in a broad pygidium.
In the next stage (which, however, is of the same date—September 10th, 1888) the
snout is truncated, and the caudal process has a dimple in the middle. Then the head
becomes defined as an oblong mass, rounded in front and flanked by the two tentacular
cirri, which now are directed forward on each side. There are still only four bristled
feet. The cilia on the scales are longer, and two short, broad, caudal cirri have
appeared under the pygidium.