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CYTHERIDEA, Bosquet.—Upper antenna (Fig. 8), robust, five-jointed and strongly spinous, the last joint narrow and elongated; lower antenna four-jointed, flagellum long and slender. Right foot of the first and second pairs in the male different from the rest, that of the first pair very strong and prehensile, of the second very feeble, the apical portion rudimentary and not clawed. Shell subtriangular, highest in front, thick ; surface smooth, closely pitted, or concentrically rugose. Hinge-joint formed by two crenulated elevations of the right valve, which are received into corresponding depressions of the left. Habitat, mostly marine.
C. elongata, Brady; papillosa, Bosquet; Zetlandica, Brady; (?) subflavescens, Brady; punctillata, Brady ; torosa, (Jones) ; lacustris (G. O. Sars); dentata, G. O. Sars.
The genus Cyprideis, Jones, is here united with Cytheridea. Of the species enumerated, all are marine excepting C. lacustris and torosa, the former of which occurs in fresh water, but seems to be excessively rare ; the latter mostly in brackish, though it has in one or two instances been found in fresh water. In the brackish pools of our salt marshes, and amongst estuarine mud, it often occurs in prodigious numbers. The powerfully chelate right foot of the first pair in the male is a remarkable character of this genus, and is interesting as showing a similarity of plan between this and other tribes of Entomostraca where the right and left limbs of the male exhibit analogous differences of structure. Somewhat similar differences occur likewise in other genera of Ostracoda, but they are especially well marked in Cytheridea. It may be noted that the male of C. lacustris has not yet been observed either in Norway or in this country, so that its place in this genus is merely provisional. Its only known British habitats are the North Shaws Loch, Selkirkshire, and the Glasgow and Paisley Canal, where it was found by Mr. D. Robertson.
CYTHEROPSIS, G. 0. Sars.-Antennæ much as in Cythere, except that the lower are much more robust. Incisive portion of the first maxilla weak, internal segment rudimentary. Second pair of maxillæ very large and much dilated at the apex, flabelliform, and beset with numerous setæ. Feet alike in male and female. Shell high and compressed in front, depressed and tumid behind; thin, pellucid, and marked with round white papillæ. Marine.
C. declivis (Norman), Argus, G. O. Sars.
ILYOBATES, G. O. Sars.—Upper antennæ very stout, fivejointed, the first two joints much thickened. Feet very short, the first two pairs three, the last four-jointed. Right foot of the last pair in the male prehensile, and only three-jointed, terminal claw very large and strong. Eyes wanting. Shell thin and pellucid, suboyate, truncate behind. Marine.
I. prætexta, G. 0. Sars.—This curious species is at once distinguished by its elongated ovate form and truncate posterior extremity, which is also centrally emarginate. It occurs very sparingly in our seas, having been found only on the Dogger Bank and on the west coast of Scotland. The absence of eyes is accounted for by its habit of burrowing in soft mud.
LOXOCONCHA, G. (. Sars.—Upper antennæ very slender, six-jointed, the last joint very long, linear, and bearing only long, simple setæ. Lowest seta of the branchial plate of first jaw deflexed. Feet long and slender, alike in male and female. Abdomen terminated by a hairy conical process; post-abdominal lobes bearing two long subequal sctæ. Shell subrhomboidal or peach-stone shaped, surface mostly marked with regular concentric pittings and small papillæ, sometimes with deep polygonal excavations; posterior dorsal angle obliquely truncate. Hinge formed by four small teeth, two on each valve.
L. impressa (Baird); granulata, Sars ; elliptica, Brady; tamarindus (Jones), guttata (Norman).
Identical with the genus Normania, described by me in the “Transactions of the Zoological Society of London,” Vol. v.: the name Loxoconcha is however of prior date. The species are all marine, except L. elliptica, which inhabits brackish water.*
XESTOLEBERIS, G. 0. Sars.-Upper antennæ six-jointed, the last four joints gradually decreasing in length and bearing very short, simple seta. Feet short, post-abdominal lobes bearing two setæ. Ova and immature young borne within the shell of the female. Shell smooth and polished, ornamented with small round papillæ, depressed in front, in the female very tumid behind." Hinge formed by a dentated crest of the left, which is received into a corresponding excavation of the right valve.
X. aurantia (Baird); depressa, G. 0. Sars.-Zenker and Sars both agree in the statement that the animals of this genus are viviparous; a point which I have myself had no opportunity of investigating.
X. depressa is a common inhabitant of deep water, while I. aurantia is found almost exclusively between tide marks. The former is pearly white, exhibiting most beautiful iridescent tints, and sometimes deeply tinged with red at the anterior extremity. The latter is yellowish brown in colour, and has no iridescence.
* The remaining genera are entirely marine.
CYTHERURA, G. 0. Sars.-Upper antennæ shortly setose, six-jointed; lower, five-jointed, terminal claws very short. Feet small, the terminal claws short and curved. Male copulative organs very complex, provided with several irregular processes and a very long spirally convoluted tube. Valves unequal and dissimilar in form, the right overlapping on the dorsal margin; produced into a more or less prominent beak behind; surface smooth or variously sculptured, mostly marked with a central areola of darker colour than the rest of the shell.
C. nigrescens (Baird), angulata, Brady; striata, G. O. Sars; lineata, Brady; cuneata, Brady; Sarsii, Brady; similis, G. O. Sars; undata, G. 0. Sars; producta, Brady; affinis, G. 0. Sars; gibba (Müller); Robertsoni, Brady ; cornuta, Brady; acuticostata, G. 0. Sars; clathrata, G. 0. Sars; cellulosa (Norman).
The members of this genus are the most minute, speaking generally, of all the Cytheridæ, and the specific differences are not always very clear; more extended observation will, doubtless, reveal many more species. Those now known inhabit chiefly deep water ; but c. nigrescens, and occasionally some others, are to be found in tidal pools. Several species are found fossil in the glacial clays. The most striking peculiarity of the genus is the production of the shell into a prominent beak or rostrum behind : the surface of the shell is often irregularly waved or ribbed.
CYTHEROPTERON, G. O. Sars.—Upper antennæ five-jointed, shortly setose, penultimate joint elongated. Feet long and slender, abdomen ending in a long, narrow process. Male copulative organs armed behind with three spiniform processes, one of which is trifurcate. Eyes wantingValves unequal, the right overlapping above, produced towards the ventral margin into a broad lateral ala, and forming behind an obtuse beak. Surface marked with shallow round or angular depressions, or with transverse ribs and furrows.
C. subcircinatum, G. O. Sars; latissimum (Norman); nodo-sum, Brady; punctatum, Brady; (?) multiforum (Norman).
A genus well characterized by the strongly projecting lateral alæ, and great tumidity, in which, however, some species
of the following genus very closely resemble it :
BYTHOCYTHERE, G. O. Sars. — Upper antennæ seven-jointed, second joint very thick, and having a single seta on each margin; the other joints much narrower, forming a slender setose lash. Mandibles constricted above the distal extremity, and bearing a well-developed branchial plate. Branchial plate of second maxilla large, numerously ciliated, the four lower cilia deflexed. Feet elongated; basal joint of the first pair bearing a small lobe, from which spring two large and two small setæ. Abdomen ending in a very long acuminate process; post-abdominal lobes narrow, bearing three hairs. Valves unequal, smooth, or sparingly sculptured.
B. simplex (Norman); turgida, G. 0. Sars.— It would not be supposed, from the external appearance of these two species, that they ought to be referred to one and the same genus; their anatomical characters, however, seem to agree closely. The former is a much elongated species, acutely pointed at the posterior extremity; the latter very tumid, subtruncate behind, and much resembling, in general contour, the preceding genus : it is pretty generally distributed, while B. simplex appears to be confined to Scotland and the northern part of England. B. simplex approaches a form described by Professor T. Rupert Jones from fossil specimens under the name Bairdia Harrisiana.
PSEUDOCYTHERE, G. 0. Sars. - Upper antennæ sevenjointed, bearing long setæ; second joint thick and armed with a single seta in front; last joint long and narrow, terminated by very long setæ : lower antennæ very slender. Mandibles small and weak. Three lowermost setæ of branchial plate of first maxilla deflexed. Feet very long and slender. Abdomen ending in a long slender process. No eye.
Shell thin and pellucid, rounded in front, produced at the posterodorsal angle.
P. caudata, G. O. Sars. This genus contains only one species, which is a very remarkable one, and apparently uncommon, The shell is subquadrangular in outline, and so much compressed as to appear almost squamous at the posterior ventral extremity, where it is once or twice minutely toothed. Colour brown, owing to the transparency of the shell, through which the animal itself is seen. Its range is extensive; the few British specimens yet taken are from Connemara, Northumberland, Shetland, and the Channel Islands.
CYTHERIDEIS, Jones.-Carapace as seen from the side, much attenuated in front, highest behind. Hinge margins nearly simple: right valve overlapping the left in the middle of the ventral surface. Animal unknown.
(. subulata, Brady.
The name Cytherideis was proposed by Professor T. Rupert Jones, for a group of species which agreed in presenting a peculiar hinge structure, the margin of one valve projecting in a sort of angular crest, the other being cut away, so as to receive it. The genus was not in any case very definite in its characters, and its members must now be looked upon as distributed amongst several other genera; but the species above-named (C. subulata) cannot at present, from want of knowledge of its anatomy, be certainly classed under any other head; the overlapping right valve precludes the notion of its belonging to Paradoxostoma, with which, in other respects, it shows considerable agreement. I therefore retain for it the name Cytherideis. This species is described by Dr. Baird as Cythere flavida, Müller ; but the two are most probably quite distinct: the latter species appears to be a yellow variety of Paradoxostoma variabile.
SCLEROCHILUS, G. 0. Sars.-Antenna robust, the lower larger than the upper; flagellum long and very slender; poison glands large and many-lobed; mouth produced, conical; labrum strongly toothed; mandible small; terminal lobes of the first pair of jaws'partially wanting; branchial plate narrow, almost lanceolate ; feet short and robust, the first pair having a strong spine at the apex of the basal joint; post-abdominal lobes very large ; valves elongated, hard, especially at the edges; surface smooth and shining.
S. contortus (Norman).-This species shows, in the strueture of the mouth and mandibles, a state intermediate between the typical Cytheridæ and Paradoxostoma.
PARADOXOSTOMA (Fischer).-Upper antennæ exceedingly slender, six-jointed and shortly setose ; lower shorter and more robust, five-jointed, flagellum very large and stout; poison glands large, lobulated; mouth suctorial ; labrum and labium forming together a large and stout subconical process, projecting downwards, and terminating in a disk, in the middle of which the orifice of the mouth is situated. Mandibles very slender, protractile, styliform; palp very slender, and without a branchial appendage. Terminal lobes of the first maxillæ very - narrow, two lower setæ of the branchial plate deflexed. Feet short and robust, last joint elongated, terminal claws short and curved; basal joint of the first pair bearing a single strong spine; one eye; shell thin and fragile, having no definite stracture; valves subequal, mostly higher in front than behind; ventral margins emarginate in front, so that when the valves are closed there is left an elongated orifice, through which the suctorial apparatus can be protruded.
P. variabile (Baird); abbreviatum, G. O. Sars; Normani, Brady; pulchellum, G. 0. Sars; obliquum, G. O. Sars; Hibernicum, Brady; Sarniense, Brady; ensiforme, Brady; flexuosum, Brady; arcuatum, Brady.
The remarkable suctorial mouth of these animals at once separates them from all other genera, and even without exami. nation of the internal parts, the shell itself gives evidence as to its affinities by the longitudinal aperture between the two valves on the anteriorportion of the ventral surface; this opening, through which the mandibles and mouth can be protruded, is