front, but irregularly wawed behind, anterior extremity gradually tapered to an 

 obtuse point, posterior abruptly truncated at the end. Valves rather uneven 

 in their posterior part, each valve being produced at the supero-posteal corner 

 to a rather prominent obtuse protuberance and having laterally 2 or 3 nodi- 

 form prominences; alaeform expansiors located somewhat in front of the middle 

 and quite simple, arcuate; surface of valves marked with rather slight scattered 

 pittings. Anterior antennae with the terminal part 3-articulate and about twice 

 as long as the distale joint of the basal part. Posterior antennae of quite 

 normal structure. Legs moderately slender, last pair with the 1st joint of the 

 terminal part about the length of the other 2 combined. 



Colour of shell not yet ascertained. 



Length of adult female 0.52 mm. 



Male, unknown. 



Remarks. In the outward appearance of the shell this form differs con- 

 spicuously from any of the other known species: but the structure of the several 

 appendages proves it in reality to be a true membre of the present genus. 



Occurrence. A single female specimen only of this peculiar form has as 

 yet come under my notice. It was found among some Ostracoda collected, 

 some years ago, at Ris0r, south coast of Norway, in depths ranging from 10 

 to 20 fathoms. 



Distribution. British Isles. 



Fossil. Scotland, Canada. 



123. Cytheropteron subcircinatum, G. O. Sars. 



(PI. CV, fig. 4). 

 Cytheropteron subcircinatum, G. O. Sars, Oversigt af Norges marine Ostracoder, p. 81. 



Specific Characters. Female. Shell rather tumid, but with the alaeform 

 expansions poorly developed, seen laterally, short oval in shape, greatest height 

 in the middle and about equal to 3 /5 of the length, dorsal margin evenly 

 arched and sloping somewhat more steeply behind than in front, ventral margin 

 very slightly sinuated anteriorly and gently convex behind, anterior extremity 

 narrowly rounded, posterior produced in the middle to a blunt prominence; 

 seen dorsally, almost circular in outline, though having the extremities some- 

 what produced, greatest width a little behind the middle and about equal to 

 2 /s of the length, side-edges evenly curved. Valves rather thin, semipellucid, 

 with the surface smooth and only marked with small scattered puncta; alae- 

 form expansions very little prominent, in the form of slight borders flanking 



