BALANUS UNGUIFORMIS. _J. de C. Sowerby_ (!). Mineral Conchology (sine
descriptione) Tab. 648, fig. 1, (Jan. 1846).
---- ERISMA. _J. de C. Sowerby_ (!). Ib., fig. 2.
---- PERPLEXUS. _Nyst_, apud D'Omalius (Sine descript. vel Tab.),
Geologie de la Belgique, 1853.[101]
[101] I am much indebted to M. Bosquet for specimens bearing this
title, from Klein Spauwen, which certainly appear to me, as far as
can be judged by the separated compartments, without the opercular
valves, to belong to our present species.
_Parietes thin, sometimes permeated by pores; radii with their upper
margins oblique; sutural edges very finely crenated: basis solid.
Tergum with the spur narrow, bluntly pointed._
_Var._ erisma, _with the walls longitudinally folded or ribbed_.
_Fossil_ in the Eocene formation, Isle of Wight, Colwell Bay;
Hordwell; Barton, (Chama Bed); Headon; Bembridge. Bergh, near Klein
Spauwen, Belgium (?). Attached to various shells and wood. Mus. J. de
C. Sowerby, E. Forbes, F. Edwards, Charlsworth, T. Wright, Bowerbank,
Tennant, Bosquet.
This species, the most ancient one as yet well known in the genus,
presents to the systematist a most unfortunate peculiarity, in the
parietes being almost as often as not permeated by small pores: I have
seen no other instance, except to a limited degree in _B. glandula_, of
this character being variable, and hence it must be still considered
of high classificatory value, in so varying genus as Balanus. Owing
to this varying condition of the parietes, together with the basis
being quite solid, our present species has as good a claim to be
ranked in the last as in the present section; indeed, I think it has
more affinity to _B. crenatus_ and _glandula_ in the last section,
than to any other recent forms: I have placed it in its present place,
owing to its intimate affinity to _B. varians_, in which the parietes
seem always to be solid; and partly, I believe, because all the first
specimens examined by me exhibited no traces of parietal pores.
Owing to the kindness of Mr. F. Edwards, I have seen the original
specimens, excellently figured by Mr. J. de C. Sowerby in the 'Mineral
Conchology:' I can perceive no difference between _B. unguiformis_ and
_erisma_, excepting that the walls in the latter are longitudinally
folded,--a character we know to be variable in so many species. In both
varieties, the parietes are sometimes porose and sometimes solid. The
smaller specimens, however, figured in the 'Mineral Conchology' to the
right hand, may possibly be a distinct species, as I infer from the
narrowness of their radii.
_General Appearance._--Shell, tubulo-conical, sometimes considerably
elongated and sub-cylindrical: surface either very smooth, or
slightly folded, or deeply folded so as to be strongly ribbed
longitudinally: orifice rather large, rhomboidal, narrow at the
carinal end, toothed, but not deeply: walls rather thin and fragile:
radii of moderate width, with their summits oblique, not quite
smooth. Basal diameter of largest specimen, about three quarters of
an inch.
_Scuta_, with the external surface smooth: there is a trace of a
furrow running down the valve from the apex, near to the occludent
margin, and this is only worth mentioning from the analogous furrows
in _B. bisulcatus_. Internally, the upper surface of the valve is
roughened: the articular ridge is very prominent, and slightly
reflexed: there is no distinct adductor ridge; there is a slight but
variable depression for the lateral depressor. _Tergum_, with the
longitudinal furrow shallow; spur moderately long, about one fourth
or one fifth of the width of the valve; placed at about its own width
from the basi-scutal angle; basal end bluntly pointed; the basal
margin on the opposite sides of the spur forms a nearly straight
line; the carinal margin has an extremely narrow border formed by
upturned lines of growth. Internally, the surface is roughened with
little points: the articular ridge is prominent: the crests for the
tergal depressores moderately prominent.
_Parietes_: the longitudinal ribs on the internal surface are either
feebly, or, in the lower part, strongly developed; their basal ends
are only just perceptibly denticulated. As already stated, in about
half the specimens, there were no traces of parietal pores; in the
other half there were either distinct or obscure pores; the pores
are circular, generally of unequal sizes, and never large; in the
same individual they would sometimes be almost wholly absent in some
of the compartments, and quite plain in the other compartments. The
Radii are either moderately wide or rather narrow, and have their
upper margins very oblique, and not distinctly arched, and not quite
smooth: their sutural edges are very finely crenated, the teeth or
septa not being denticulated. The upper margins of the _alæ_ are
rather less oblique than those of the radii: their sutural edges are
barely crenated. The _basis_ is thin, and without any trace of pores;
the upper surface is sometimes furrowed in radiating lines.