RECENT BRITISH OSTRACODA. 



363 



Monoculus aurantius, Jurine, Hist, des Monocles, p. 173, pi. xviii. figs. 5-12. 

 ruber, Idem, ibidem, p. 172, pi. xviii. figs. 3, 4. 



Valves oblong, subreniform, narrowed in front. Anterior extremity narrow, bordered 

 by a flattened encircling lamina ; posterior broad and well rounded. The ventral margin 

 is straight or slightly sinuated ; the dorsal arched, highest at its posterior third. Seen 

 from above, the carapace is oblong, ovate, tapering to the anterior extremity, which is 

 acutely pointed, the right valve being considerably overlapped by the left. Tront view 

 ovate, the suddenly compressed anterior margins projecting sharply forward. The surface 

 is indistinctly granular, and finely punctate. Colour ochreous yellow, marked with 

 bands and blotches of deeper orange. Near the anterior third of the dorsum there is 

 frequently a conspicuous deep-brown or black spot, marking probably the position of the 

 eye. The arrangement of the antennal setas is precisely like that of C. virens, — the upper 

 antenna bearing nine long and several shorter plumose filaments ; the lower five, which 

 reach but slightly beyond the apices of the claws. Eour much shorter and mostly 

 non-plumose setae rise from the middle of the fourth joint, and reach not very much 

 beyond the bases of the claws. These are found in all members of the genus. Setae of 

 the abdominal rami four, the two shorter ones being much longer than those of C. fusca 

 or 0. virens. The anterior portion of the shell is not unfrequently studded with a 

 number of minute tubercles, which along the margin are gathered into a regular row 

 of from twenty to thirty (fig. 21), producing an appearance as of a finely crenated or 

 serrated border. The marginal row of tubercles is present, however, only on the right or 

 smaller valve, which is provided internally with a narrow laminar plate (fig. 22), and is 

 received within the overlapping and perfectly simple margin of the left valve. The pos- 

 terior margin is also occasionally, but less frequently, tuberculated in a similar manner. 



Length i^i-j height g^j- in. /. K.s-i 



C. incongruens seems to be one of the less common species of this genus. It has 

 been found in Kent and Essex by Professor T. Rupert Jones, at Blackheath, Windsor, 

 and Dover by Dr. Baird, in the island of C umbrae and in a lagoon on the Ayrshire coast 

 by Mr. D. llobertson, in the county of Durham and in the Isle of Arranmore (Galway) 

 by myself. It has a wide range on the continent, being mentioned by various authors 

 as occurring in Switzerland, Germany, Norway, and Sweden. 



My figures and description of this species were completed before I became acquainted 

 with the memoir of Pischer contained in the ' Transactions of the Munich Academy ; ' 

 and it is satisfactory to find that the observations of that author as to the distinctive 

 characters of C. aurantia are quite in unison with my own. Dr. Pischer, however, 

 assigns a specific rank to C. rubra, Jurine, almost entirely on the ground of the want of 

 tuber culation of the carapace, at the same time admitting that the subject wants investi- 

 gation, and that the relations between C. fusca, C. aurantia, and C. rubra are far from 

 being clearly made out *. Prom what has been said above, it will be seen that I regard 

 the two former species as distinct, not only from characters afforded by the carapace, but 



* Es muss iibrigens erst weitere Beobachtung lehren, ob nicht Uebergangsformen zwischen C. aurantia, fusca und 

 rubra stattfinden, und sie alle drei nur als eine Species zu betrachten sind, da ihr Korperbau durchaus keine weseut- 

 Uche Verschiedenheit wahrnehmen lasst." 



3 D 2 



