of ihe North Atlantic and of North- Western Europe. t\.Z 



Professor G. 0. Sars long ago described, though he did not figure, the 

 remarkable resemblances which exist between some of the limbs of Cytherella and 

 those of certain otlier Entomostraca belonging to the widely separated orders of 

 Branchiopoda and Copepoda. The resemblance, for instance, is at once apparent 

 between the extraordinary doubly branched antenna of Cytherella and the thoracic 

 swimming-feet of many of the Copepoda. The appendages of the mandibles and 

 first pair of maxillae, on the other hand, with their profuse armature of immensely 

 long, pectinately arranged setse, are wonderfully like the feet of the Sididce. 

 Another interesting point which seems hitherto to have escaped notice is the 

 division of the posterior part of the body into numerous distinct segments, so that 

 the abdomen of the animal recalls in its general aspect the tail of a lobster, or 

 perhaps of some Branchiopoda such as Chirocephalus. Except by G. 0. Sars, no 

 example of Cytherella have yet been observed in the living condition ;* and in the 

 European area, at any rate, it has never been taken except in considerable depths, 

 nor in the tow-net either in the depths of the sea or at the surface. It may be 

 assumed, therefore, though the profuse setose armature of the antenna would seem 

 to adopt it for swimming, that it does not usually leave the bed of the sea to any 

 great distance. Several recent species (about sixteen) have been described from 

 various parts of the world, but except in the case of C. ahyssorum and C. serrulata, 

 the shell only has been seen. Numerous fossil species have also been recorded, 

 but it is doubtful whether in some cases these species may not really belong to 

 other genera. 



1. Cytherella serrulata, n. sp. 



(PI. Lxvi., figs. 3-6, 9-16; PI. lxvii., figs. 15, 16.) 



Shell of the female, seen from the side, subovate, almost reniform, a little 

 higher in front than behind, greatest height equal to more than half the length ; 

 anterior extremity broadly and evenly rounded, sometimes slightly serrulated, 

 but usually entire ; posterior narrower, sloping rather steeply above, but broadly 

 rounded below, and (in the adult female) fringed with a series of numerous 

 minute teeth ; dorsal margin straight, or very slightly arcuate, sloping gently 

 downwards towards the posterior extremity ; ventral distinctly sinuated in the 

 middle. Seen from above, compressed, ovate, widest behind the middle, width 

 equal to rather more than one-third of the length, subtruncate behind, with 

 rounded angles, and tapering with a gentle curve towards the front, which is 

 subacuminate. Surface of the valves smooth and polished, except the posterior 

 extremity, which is roughened with numerous minute spines. Shell of the male 

 much more compressed, and without marginal teeth. Seen from above, it is of 

 almost equal width throughout, and quite thrice as long as broad ; subtruncated 



* This was written before the publication of G. W. Miiller's monograph. 



