from the Arctic and Scandinavian Seas. 



35 



pits, and having a sharply angular ridge or crest just within 

 and parallel to the ventral margin. Colour white. Length 



1 



62 



inch. 



Two specimens only in the gathering from Davis's Straits. 

 In shape these agree very closely with Sars's C. atra ; but the 

 sculpture and colour of the shell would seem to be different. 

 The description " valvulse distincte et sat regulariter reticulata3, 

 areola mediana obsoleta. Testa tota colore saturatissime atro 

 insignis " does not apply here. The sculpturing of G. rudis^ 

 is too decided to be called mere reticulation ; and there is no 

 trace of coloration of any kind in om* specimens. 



EXPLANATION OF THE PLATES. 

 Plate IV. 



Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 



1. Q/^/jere Jwea/is (female), from left side. \ 



2. The same, from above. 



X40. 



X84. 



3. The same (male), from left side. 



4. The same (male), from below. 



6. The same, outline of left valve (female). 



7. The same, outline of right valve (female). 



5. CytJiere liobertsoni (female), seen from left side. 



8. The same, seen from above. 



9. The same, seen from below. 



10. The same, seen from front. 



11. Pontocypris atteiiuata, seen from left side. 

 Fig, 12. The same, seen from above. 



Fig. 13. The same, seen from below. 

 Fig. 14. The same, end view. 



[The description of Pontocypris attenuata (a southern species) 

 will be given in a subsequent paper.] 



Plate V. 



Fig. 1. Cytheropteron montrosiense (adult female), seen from 

 left side. 

 The same, seen from above. 

 The same, end view. 

 The same (young ?), seen from left side. 

 The same, seen from below. 

 Cytheropteron vespertilio, right valve, seen from outside. 



Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 10, 

 Fig. 11, 

 Fig. 12, 

 Fig. 13, 

 Fig. 14 

 Fig. 15, 

 Fig. 16 

 Fig. 17, 

 Fig. 18, 

 Fig. 19 

 Fig. 20 



XoO. 



The same, seen from above. 



Cytheropteron injlatum, right valve, seen from outside. 



The same, seen from above. 



The same, end view. 



Cytheropteron pyramidale, seen from left side. 



The same, seen from above. 



The same, seen from below. 



The same, seen from behind. 



Cytherura rtidis, seen from left side. 



The same, seen from above. 



The same, seen fi*om the front. 



Cy there pukheUa (female), seen from left side. ) 



Thft sanifi. sften from abovfi. ^ 



The same, seen from above. 

 The same, seen from the front. 



I 



X40. 

 3* 



