257 



pointed. Valves semipellucid, with the surface very smooth and polished, 

 wanting any obvious sculpture, edges almost bare of hairs, but bordered with 

 a narrow hyaline rim. Eye rather large and well conspicuous in fresh speci- 

 mens. Anterior antennae moderately slender, with the 2nd joint of the terminal 

 part slightly longer than the 1st, the last 2 joints combined exceeding half the 

 length of this joint. Posterior antennas with the dividing suture of penultimate 

 joint located about in the middle, apical claws very short; vesicle leading to 

 the flagellum rather large, clavate in shape. Mandibular palp not much pro- 

 longed, with the terminal joint comparatively short. Maxillae without any trace 

 of a palp. Legs rather slender, but with the apical claw comparatively short 

 and stout. 



Male of rather larger size than the female, with the shell comparatively 

 more elongate in shape. Copulative appendages coarsely developed, with the 

 basal part very large and expanded; terminal part represented by 2 diverging 

 pieces, the anterior one spiniform and slightly tortuous, the posterior somewhat 

 larger and lamelliform, terminating behind in an acute corner. 



Colour of shell somewhat variable, but more frequently light yellowish 

 or whitish, with 2 sharply defined patches of a dark violaceous or almost black 

 hue on each side, the one about in the middle, the other near the posterior 

 extremity, a 3rd less sharply defined patch being moreover generally present 

 in the oral region of the shell. 



Length of adult female amounting to 0.60 mm., of male to 0.68 mm. 



Remarks. The present species, being that recorded at the earliest date, 

 ought of course to be regarded as the type of the genus Paradoxostoma. It 

 is easily recognised from the other known species by the characteristic cunei- 

 form shape of the shell, as seen laterally, and also partly by the colour. 



Occurrence. This is one of our commonest Cytheridae, occurring very 

 abundantly along the whole of the Norwegian coast in the littoral zone among 

 algae, and often left in tidal pools together with other littoral animals. 



Distribution. British Isles, Holland, Arctic Ocean: Baffin Bay, Hunde 

 Island, Spitzbergen. 



Fossil. Norway, Scotland, Ireland, Canada. 



32 Crustacea. 



