153 



like spines; the posterior ones with the flagellum well developed, and with 3 

 apical claws on the terminal joint. Vibratory plate of mandibular palp more 

 fully developed than in the other genera. Maxillae with the masticatory lobes 

 rather short and stout. Legs comparatively robuste, with a slight rudiment of 

 a proximal bristle on the front edge of the basal part, and with the seta on 

 the infero-posteal corner remarkably developed. Caudal rami forming 2 oval 

 thickened pieces placed vertically, and each provided behind with 2 extremely 

 small simple bristles. Genital lobes remarquably produced below. Reproduction 

 exclusively parthenogenetical. 



Remarks. This new genus is established, to include the form at first 

 recorded by the present author as Cythere lacustris, and subsequently generally 

 referred to the genus Chyteridea of Bosquet. On a closer examination of the 

 said form, I have found it to present some rather notable particularities 

 distinguishing it both from Cytheridea and from the nearly-allied genus 

 Cyprideis, and have therefore felt justified to keep it apart from both these 

 genera as the type of a separate genus. 



66. Cytherissa lacustris, G. O. Sars. 



(PI. LXX.) 

 Cythere lacustris, G. O.. Sars, Zool. Reise i Sommeren 1882, p. 30. 



Syn : Cytheridea lacustris, Brady. 

 Acanthopus resistans, Vernet. 

 , Cyprideis torosa, Jones (part). 



Specific Characters. Female. Shell rather tumid, seen laterally, oval 

 subtriangular or somewhat clavate in shape, much higher in front than behind 

 greatest height about equalling 3 /s of the length, dorsal margin forming above 

 the eyes a gibbous prominence, thence sloping obliquely backwards and joining 

 the hind edge by an abrupt bend, ventral margin slightly sinuated in front 

 of the middle and curved evenly upwards behind, anterior extremity broadly 

 rounded off, posterior much narrower and obtusely blunted at the end; seen 

 dorsally, irregularly oval in outline, with the sides waved, greatest width about 

 half the length, both extremities obtuse at the end and nearly equal. Surface 

 of shell very uneven, exhibiting on each side 3 or 4 more or less conspicuous 

 obtuse protuberances and on the ventral face a number of irregularly waved 

 longitudinal ridges. Valves very solid and but little pellucid, being sculptured 

 with densely set irregular pittings and scattered tubercles, each composed of a 

 group of small nodules; marginal zone very narrow and indistinctly striated, 

 edges smooth and clothed with fine hairs. Anterior antennae with the basal 



19 Crustacea. 



