RECENT BRITISH OSTRACODA. 



inferior nearly straiglit. Seen from above, the outline is compressed oval, the sides 

 nearly parallel in the middle, extremities evenly tapering ; width equal to less than half 

 the length. Eight valve much overlapping the left. Shell marked with a few large and 

 deep polygonal or irregularly rounded excavations, each of which has a small elevated 

 nodule at the bottom ; colour yellowish ("in medio vero colore saturate fusco-violaceo 

 insignis," Sars). 



Length in. ' ' 

 Hab. Birterbuy Bay and in shell-sand from Donegal and Roimdstone Bays (G. S. B.) ; Lamlash, Ber- 

 wick, Gruernsey, Arran (Ireland), and in rock-pools, Arran, N.B. {Rev. A. M. Norman) ; Cumbrae 

 and Shetland [Mr. D. Robertson). 



This is the smallest of the genus, and almost the smallest of British Ostracoda. It is 

 also a very distinct and well-marked species, having no near allies except C. clathrata, 

 with which, however, it is little likely to be confounded. 



Genus 9. Cttheuopteeon, G. O. Sars. 



Valves unequal and of dissimilar form, the right overlapping the left in the middle of 

 the dorsal margin; surface marked with small round impressed puncta or shallow 

 angular pits, sometimes with elevated ribs ; ventral surface expanded laterally into a 

 winged process ; posterior margin produced into an obtuse beak. Hinge-joint composed 

 of two terminal teeth on the right valve, and on the left a median crenulated ridge. 

 Upper antennge shortly setose and composed of five joints, penultimate joint elongated 

 and bearing on the middle of the anterior margin two hairs ; lower antennas distinctly 

 five-jointed, flagellum long. Mandibles of moderate size; palp three-jointed, branchial 

 appendage bearing two very small setse. Jaws as in the preceding genus. Eeet long 

 and slender, terminal claw slender. Abdomen ending in a long, narrow process, post- 

 abdominal lobes bearing three short hairs. Copulative organs of the male armed behind 

 with three spiniform processes, one of which is trifurcate. Eyes wanting. 



This genus is easily distinguished by the prominent lateral alse of the shell; the 

 peculiar armature of the male copulative organs is a remarkable characteristic of the 

 internal animal structure. 



1. Cttheropteron suBcmciNATTJM, G. O. Sars. (Plate XXXIV. figs. 39-42.) 

 Cytheropteron subcircinatum, Gr. O. Sars, loc. cit. p. 81. 



Very similar to the following species, but smaller ; the lateral alse almost semicircularly 

 curved, and not angular. Carapace, as seen from the side, subovate ; highest in the middle, 

 greatest height equal to more than half the length, obliquely rounded in front ; posterior 

 margin somewhat angularly produced ; superior margin forming a flattened arch ; inferior 

 nearly straight, but encroached upon by the convex margin of the lateral ala. Outline, 

 as seen from above, very broadly ovate, widest in the middle ; greatest width equal to 

 two-thirds of the length, extremities very slightly mucronate. End view triangular, 

 width greater than the height, sides convex, base slightly concave ; valves unequal. 

 Surface of the shell faintly pitted, ventral surface longitudinally grooved and bearing a 



