248 





deep incision and somewhat widening distally, with the extremity rounded off 

 and slightly angular behind. Caudal lamellae well observable immediately below 

 the copulative appendages, and notably differing from those in female by the 

 great size of the anterior lobe. 



Colour of shell whitish, semipellucid, with a dark patch dorsally behind 

 the ocular region. 



Length of adult female 0.80 mm. 



Remarks. This form was recorded as early as the year 1862 by Norman 

 as a species of Cythere, and was subsequently described by the present author 

 as the type of his genus Sclerochilus. The form recorded by G. W. Mtiller 

 under that name from the Gulf of Naples is a different species, viz., S. abbre- 

 viates, Brady. 



Occurrence. I have taken this form not unfrequently in several places 

 on the Norwegian coast, from the Oslo Fjord to Finmark, in depths ranging 

 from 10 to 30 fathoms. 



Distribution. British Isles, Arctic Ocean: Greenland, Spitzbergen, Franz 

 Joseph Land. 



Fossil. Norway, Scotland, Ireland, Canada. 



Gen. 50. Paracytherois, G. W. Muller, 1894. 



Generic Characters. Shell thin and fragile, much compressed, and of 

 more or less elongate shape, with the marginal zone of the valves com- 

 paratively broad and crossed by distant somewhat irregular pore-channels. 

 Hinge-line of right valve with traces of closing teeth in front and behind. 

 Eyes wholly absent. Anterior antennae very narrow, with the segments of the 

 basal part not at all dilated, terminal part only composed of 3 joints clothed 

 with scattered comparatively short setae. Posterior antennae with the penul- 

 timate joint distinctly subdivided and provided with a small setiferous ledge 

 anteriorly, last joint with a single apical claw accompanied by a small bristle. 

 Oral cone projected almost straight forwards and terminating in an acute 

 beak-like point, lips partly coalesced. Mandibles simple stylifonn, in some 

 cases projecting long beyond the oral aperture, palp rudimentary. Maxillae 

 with 2 very narrow masticatory lobes, palp shorter than these lobes, vibratory 

 plate with 2 thin deflexed setae at the base. Legs rather narrow, with the 

 last joint considerably prolonged. Caudal lamellae very small, with only a 

 single bristle at the base. Copulative appendages of male with the terminal 

 part more or less imperfect. 



