104 DORIS TBSTUDINARIA.
or absence of the labial armature in various species. There certainly seems to be ground
for suspecting that in some species of Doris it is generally absent, but occasionally present,
though not much developed. With reference to this and many other organs, we have
little information as to the effect of age and growth on the external and internal characters
of Nudibranchs.
GEITODORIS PLANATA A. & H.
Alder 1, p. 85; Gr&rstang 2, pp. 445—446.
Alder and Hancock’s Doris planata has been attributed to the genus Platydoris by
several authors who in so doing seem to have attended only to the description given
opposite the plate and to have neglected the definitions of characters given in the
synopsis at the end of the Monograph (pt. vii, p. 42). D. planata there comes under the
heading:
“ * *O ral T entacles linear.
“ Lingual spines of two kinds, various: no central spines. Occasionally with a spinal
buccal collar.”
From this it follows that the animal has a radula with differentiated teeth of two
kinds and may have a labial armature. Such an arrangement is not characteristic of
Platydoi'is, which is distinguished by a peculiar hard texture~and by a special armature
on the genitalia, features which have not been found in any British species. At present
there is no reason to include Platydoi’is in the British fauna, though it is common in the
warmer parts of the Atlantic and Mediterranean.
I have examined the specimen kept in Alder and Hancock’s collection at
Newcastle labelled “ Doris planata, W. R. Hughes, Sidmouth.” I t is not the specimen
from which the description in the Monograph was made, for that animal, we are told, was
captured in Lamlash Bay, but it is labelled by Hancock and evidently put in the collection
to represent the species, so it must, I think, be regarded as the type specimen. I t is only
5 mm. long and 4 mm. broad and entirely dried up, having unfortunately not been kept
in alcohol. As far as anything can be made out under such unfavourable conditions, the
external characters are much as in Alder and Hancock’s plate. The colour is yellowish,
the back granulate and pitted, the mantle edge very ample, the branchial pocket large
and round. There is a distinct yellow labial armature composed of rods. As usual in
these old specimens, the radula is decomposed and in confusion, but there are clearly
visible (a) ordinary hamate teeth, (b) bundles of long, thin, almost shadowy teeth. The
whole animal is very flat.
I have examined seven preserved specimens of the form known in the laboratory at
Plymouth as D. planata but have not seen any alive. They appear to be of the same
species as Alder and Hancock’s specimen mentioned above, and have the following characters
: (1) The dorsal integuments are spiculous and the surface is granulate with tubercles
and pits which impart to it as a rule a honeycombed appearance. (2) The anterior margin
GEITODORIS PLANATA. 105
of the foot is deeply grooved and the upper lamina notched in the middle. The tentacles are
distinct and conical. (3) The rhinophorial and branchial pockets have slightly raised
rims, which bear small tubercles but are not lobed. The branchiae are small and vary from
six to nine in number. (4) There is a labial armature consisting of an almost complete
ring of short closely packed brown rods. The maximum formula of the radula is about
18 x 10 + 1 4 . 0 . 1 4 + 10* The fourteen teeth (or fewer) which are nearer the rhachis
are of the ordinary hamate type. The ten outermost are extremely thin and closely
crowded. (5) No prostate was found and no armature in the genitalia.
These data appear to me to show that the Doris planata of Alder and Hancock
is referable to the genus Geitodoris. But as already indicated in discussing D. testu-
dinaria an uncomfortable doubt hangs about the species, though for purposes of
nomenclature I think the evidence of the type specimen is decisive. But in 1869
Alder contradicted the statements made in the Monograph and declared (Alder 1, p. 85)
that “ the examination of further specimens of different sizes from the Clyde district
proves that D. planata of the British Nudibranchiate Mollusca is the young of D.
testudinaria.” Either Alder’s statement is incorrect or else the mouth parts of the species
vary at different stages of growth, a labial armature being present in young individuals,
but disappearing, at least as a rule, in adults.1
I do not understand Garstang’s description of the radula (l. c.). Either he must
have chanced on a monstrosity in which the teeth were fused together, as sometimes
happens, or he must have been misled by the bundles of thin teeth, which often look as
if they were united together.
ALDISA ZETLANDICA A. & H.
(Plate I, figs. 3 and 4.)
Bergh 38, p. xxxviii; id. 16, pp. 348—352 ; id. 53, pp. 7—10; id. 54, pp. 5—7. G. O. Sars 1,
p. 305 and plate 27.
From the rough notes at the side of Hancock’s drawings it would appear that they
were made from two specimens. Of one it is said—“ Doris zetlandica, Mr. Norman,
Shetland. Plumes six, bipinnate, perhaps imperfectly tripinnate. Tubercles of various
sizes and shapes. Tentacles (i. e. rhinophores) retractile. The margins of the cavities set
with four to five tubercles. Colourless or yellowish white.” It is not quite plain if this
last phrase refers to the whole animal or to the tubercles only. Of the other specimen it is
said—“ Dredged off Shetland by Mr. Barlee. Tubercles large, distant, soft, papillose:
small ones interspersed : linear, obtuse, but probably pointed when alive.”
The species seems rare, but is recorded within the limits of the Azores in the south
and latitude 66’33° N. I have never had an opportunity of seeing it alive, and as far as
I am aware it has not been caught at any of our biological stations. The best and most
detailed descriptions are by Bergh (53 and 54), from which the following details are
extracted. Bergh has also reproduced a sketch of the living animal (53).
1 Yayssi&re’s statement that it is present in the adults of the species which he calls Arckidoris
stellifera must, however, be remembered.