DENDEONOTUS SsACTEUS Thompson.
See Ih'itonia lactea Thompson in Ann. Nat. Hist., vol. v, p. 88.
This form is dismissed as a variety of B. arborescens both in the Monograph and by
Alder (1, p. 63), but E. Becker (Mollusk. von Jan Mayen, 1886, p. 14) maintains that it
is a distinct species, characterized not only by its milk-white colour but by differences
in the frontal appendages and the radula. He says that it bears on the frontal v.eil four
appendages in the upper line and two smaller below, in the middle. The median tooth
of the radula is smooth, not denticulate as in B. arborescens, and the formula is 6 or
7 + 1 + 6 or 7, whereas in B. arboi'escens it is 9 or 10 + 1 + 9 or IQ, These lateral teeth
have short hooks and bear three denticles.
I have not had an opportunity of seeing this form.
LOMANOTUS V érany, 1844.
Alder and Hancock, Monograph, Fam. 3, genus 10 (under name of Eumenis). Garstang 1,
pp. 185—189. Beaumont 1, pp. 842—844. Colgan in Ann. and Mag. Nat. Hist.7-1908,
vol. ii, pp. 2Ó5—218.
The members of this genus are not common, and large-specimens are rare, though
small ones are not infrequent in some localities, e. g. Plymouth. The body appears to be
very delicate and easily torn, and most authors report that their specimens were badly
preserved. The following species have been described:
Jl. Lomanotus genei Vérany, Catal. degli. anim. invert, di Genova e Nizza, 1846.
1.2. L. liancoclci Norman, Ann. Mag. N. H., vol. xx, 1877, p. 5187
8. L. portlandicus Thomps., Ann. Mag. N. H., vol. v, 1860, p. 50.
14. L. eisigii Trinch., Rendic. Acc. Sci. Pis. Mat., xxii, 8, 1883, pp. 92—94.
5. L.flavidus A. & H., Monograph, Fam. 3, pi. 41.
6. L. marmoratus A. & H., Monograph, Fam. 3, pi. 1.
7. L. vaiians Garstang, l. c.
Of these names the last is proposed by Garstang for all the British species
(L. marmoratus, L. flavidus, L. portlandicus, and L. liancoclci), on the supposition that
they are really one. But if that supposition is correct, the right course would seem to be
not to introduce a new name, but to call all the forms by the earliest of the existing
specific names. L. varians may therefore be omitted from the list. The remaining six
forms may be divided into the large and the small. Of the large forms L. genei has
undoubted priority as a name, and it is unfortunate that the authors of the remaining
three large species, L. liancoclci, L. poi’tlandicus, and L. eisigii, did not, in describing them,
state definitely in what points they considered them to differ from the typical species.
I t seems certain that the number of processes on the frontal veil and on the rhinophore
sheaths differs in otherwise similar individuals and cannot be made a specific character.
L. portlandicus is not distinguished from L. genei (l. c.) by any clear character. Norman
states that the most marked character of his L. liancoclci is “ the small size of the terminal,
simple, conical process, which is projected beyond the calyx-like sheath ” of the rhino-
phores. But it is highly probable that the rhinophores were of the usual type, and that
the lower laminated portion was merely hidden withinv the sheath. Trinchese (Z. c.) has
given a somewhat detailed description of L. eisigii, from which it appears that its most
remarkable characters are : (1) that the hepatic diverticula do not extend into the marginal
papillæ ; and (2) that the two margins unité at the end of the body and form “ una larga
pinna che è 1’ organo principale del nuoto.” But a similar organ is found in the specimen
described below, and is figured in some unpublished drawings of L. portlandicus made by
Hancock, and preserved in the Newcastle Museum. Alder and Hancock, as well as
Bergh, found the hepatic diverticula in the papillæ, but I could not demonstrate their
existence with certainty in the specimen which I examined. I t is possible that different
specimens may vary in this respect, as do Bendronotus-and Bornella excepta. Trinchese
also states that in the young L. eisigii, “ Ogni papilla conteneva un lobo epatico bene
sviluppato.”
While the present work was going through the press, I received a copy of a paper,1
in which Mr. Farran expresses the opinion that there are two large species of Lomanotus
found in British waters, namely, L. genei and L. portlandicus, characterized as follows.
The colour of L. genei, though variable, is always deep and, it would seem, usually
crimson, flecked with white spots. The maximum formula of the radula is 32 x 36.0.36.
The verge is long (about 10 mm.) and uniformly tapering. In L. portlandicus “ the general
coloration of the body is transparent white, Suffused with pale orange red. The papillar
fringe is basally of an orangé red colour, the tips of the papillæ being opaque white. The
only variation in colour to which this form is subject tends to a suppression of the orange
red coloration, which is occasionally entirely absent.” The radula attains a maximum of
42 X 58.0.58, although the animal is rather smaller than L. genei, and the verge is short
and thickish (about 6 mm. by 1 mm.).
Mr. Farran admits that the “ differences in colour would not be sufficient to maintain
the soundness of Thompson’s species,” and the specific validity of the other characters is
questionable, for the radula in Lomanotus is peculiarly difficult to count, and in all Nudi-
branchs the shape and size of the verge vary according to the retracted or exserted condition
of the organ. But my own investigations do not support Mr. Farran’s theory that
these characters are.always grouped together in the way he describes. After reading his
paper I dissected a specimen captured at Plymouth in 1908 which in life was white,
suffused with orange red, and which still shows that the base of the papillar fringe was
reddish and the tips of the papillæ white. In coloration, therefore, it is L. portlandicus.
But the formula for the radula does not exceed 32.1.32a and the verge is thin and
slightly tapering. It is 8 mm. long and only '5 mm. broad at the base, so that it is almost
thread-like. Thus in these two characters the animal is L. genei. While not wishing to
1 Farran 2.
2 In Lomanotus the teeth in the middle part of the radula are rather widely spaced, but if a given
vertical space be taken as representing the rhachis the number of teeth on the two sides of it is often
not the same. I am inclined to believe that there is a rhachidian tooth, but that in most cases it has
ceased to be strictly central in position.