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Sub-Genus Siphonostra n. sub-gen.
Description: —Shell: — This is elongated and lias a well-developed, beak-shaped
posterior process. The rostral incisur is deep and narrow. Near the inner edge of the incisur there
are two medial bristles situated close to each other. Posteriorlv, within the posterior margin of
the shell, the list is not developed. Seen from inside, the posterior beak-like process appears
to have thin walls and to be constructed in such a way that when the two valves are close to
each other a rather wide tube, a siphon, is formed, a character which gives the sub-genus its
name. Witli rather strong calcification. The forms are of moderate size.
First antenna: — This is comparativelv short and moderately siender; witli eight
joints; the proportions between the joints differ rather slightly from those given in the diagnosis
of the sub-family; cf. the description of the species. The sensory bristle of the fifth joint has
a comparativelv small number of sensory filaments (always fewer than thirteen?).
Second antenna: — The protopodite has a medial-distal bristle. E x
o-p o d i t e: The bristle of the second joint is rather strongly developed. Some of the natatorv
bristles of the following joints have, in addition to natatorv hairs, powerful spines as well.
The third to the ninth joints have basal spines. The e n d o p o d i t e is reduced. (Similar
in the males as in the females? Cf. below that Cypridina hirsuta C. \Y. Müller may possible
belong to this sub-genus.) The bristle of the end joint is long.
M â n d i b 1 e: — Proto p o dite: The endite on the coxale is rather weakly bifur
-cated distally, furnished with a rather powerful equipment of spines especially mediallv-distally;
the spines only with rather a slight tendenev towards arrangement in groups. This joint has
no bristle except the small one on the endite. Basale: Of the ventral bristles one d-bristle is
very long, with numerous long secondary bristles at the middle arranged in irregulär
groups and with short hairs distally; the other ventral bristles on this joint are more
or less short and have short hairs or are bare. This joint has three bristles dorsally.
En dop o di te: The first joint has four bristles ventrally. The end joint has seven
bristles, of which the two middle ones are powerful and claw-shaped and of about the
same length and strength.
Maxilla: —• Protopodite: The coxale has distallv a single bristle with short,
fine hairs or almost bare. Proximally on the outside of the third endite there is a single bristle.
On the boundary between the basale and the first endopodite joint there are three bristles,
one close to the exopodite, one at about the middle of the inside of the palp and one on the
anterior edge of the latter. Dorso-distally on the coxale there is a rather large and somewhat
lamelliform epipodial a p p e ndag e. The exopodite is comparatively well
developed and has close, fine, long hairs; it is not displaced distally. The endopodite is
very wide and of moderate length.
Si x t li 1 i m b: — The second exopodite joint is very short, broader than it is long,
furnished with rather few bristles; the posterior ones of these bristles are not strikingly larger
than the others.
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