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an almost symmetrical rostrum, posteriorly it is somewhat pointed. The shoulder vault is
well developed, but is always rounded. To judge Iront the literature the surface
sculpture varies: G. 0. Sars writes, 1865, p. 117: „striis numerosis densissimis et decussatis
reticulatae“; G. W. MÜLLER, 1901: „Bisweilen zeigt die Schale eine deutliche Streifungi Meist
erkennt man als Rest einer Streifung nur eine Zähnelung resp. Felderung an der vorderen Hälfte
des Ventralrandes, und auch diese kann fehlen“. Cf. also V. Vävra, 1906, p. 42. The specimens
investigated by me showed an agreement with G. 0. Sars’s original description with regard
to this character, but the réticulation was sometimes rather difficult to verify. The variation
is perhaps only apparent; cf. G. W. MÜLLER, 1906a, p. 33. The surface of the shell
is without or practically without hairs. Seen from inside: Selvage: This is in most
cases smootfnedged on the rostrum and has no spine-like process. It is quite smooth-edged or
sometimes exceedingly finely serrulated along the anterior margin of the shell and the
anterior half of the ventral margin of the shell; it is finely serrulated along the posterior half of
the ventral margin of the shell and along the ventral half of the posterior margin of the shell.
There are compound glands as described by G. W. MÜLLER, 1906 a. The glands along the
posterior margin of the shell are moderately large and have their exits on the margin of the shell
itself; only one or a few emerge (with a simple exit) between the list and the margin of the shell.
There is no hinge-socket or hinge-tooth at the postero-dorsal corner of the shell.
First antenna: — The first joint is comparatively long and has in most cases
a rather distinct contraction near the base; cf. the accompanying fig. 14; the proportion between
the lengths of the first and second joints is about 8 : 5. The b-, d- and e-bristles are in most
cases subequal and somewhat shorter than this limb. E-bristle: This bristle has at about
two-thirds of the way along it an oval plate like a suctorial organ of about the type reproduced
in fig. 15; the edge of this plate is — at least as far as I could observe — smooth. Just distally
of this plate there is a somewhat varying number of short and rather powerful spines, arranged
in two groups situated near each other; the number of spines is most frequently about the same
as in the accompanying fig. 15. Just distally of these spines this bristle is in most cases bent
at a distinct angle. The part of the bristle distally of these spines is closely and finely annulated
or partly hyaline, bare, and is not at all or only slightly widened. (Note that the proportion
between the sucker-like plate and the part of this bristle situated distally of this is quite incorrect
in G. W. Müller’s work of 1901.) The part of this bristle situated proximally of the sucker-like
plate is furnished on its anterior side with sparse and exceedingly short bristles (scarcely
perceptible with Reichert’s ocid. 4, Leitz’s immersion V,2). B- and d-bristles: These seem sometimes
to be quite bare, sometimes one or both of them bas a rather small number of short, moderately
strong or rather weak spines about opposite the sucker-like appendage of the e-bristle. The
distal part of these bristles is of about the same type as that of the e-bristle; the bending into
an anule is about the same as in the latter bristle or in most cases somewhat weaker. None of
O
these three bristles has distinct pad-like formations; it is to be noted, however, that their distal
parts have in certain positions a structure that reminds one rather stronglv of such formations.
The a-bristle is very long, in most cases about as long as or somewhat shorter than, sometimes
even somewhat longer than the b-, d- and e-bristles; in most cases it is more or less straight,
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