225 

 

 118. Cytheropteron alatum, G. O. Sars. 



(PI. CIV, fig. 1). 

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



Specific Characters. Female. Shell exhibiting a very peculiar appearance 

 on account of the excessive development of the alaeform expansions, seen 

 laterally, narrow oblong in shape, greatest height in the middle and scarcely 

 exceeding half the length, dorsal margin gently arched throughout, ventral 

 very slightly sinuated, anterior extremity obtusely rounded off, posterior pro- 

 duced in the middle to a well-defined protuberance somewhat obliquely trun- 

 cated at the end; seen dorsally, very broad, square-shaped, with the width 

 between the tips of the alaeform expansions fully attaining the length, both 

 extremities narrowly produced. Valves thin and pellucid, without any obvious 

 sculpture, alaeform expansions remarkably large and prominent, extending 

 somewhat downwards, and triangular in shape, each exerted at the end to a 

 sharp spiniform process, posterior edge of the expansion provided with a row 

 of peculiar appendages, the 2 proximal ones somewhat remote from the others 

 and lamelliform, being divided at the end into fine points; inner duplicatures 

 of the valves rather broad and crossed by scattered fine pore-channels. An- 

 tennae of a structure very similar to that in the preceding species. Legs 

 extremely slender and narrow, with the apical claw much prolonged. Posterior 

 end of body produced in a remarkably long conical process. 



Male of rather smaller size than female, but resembling it in the general 

 shape of the shell. Copulative appendages built on the same type as in C. 

 latissimum, but with the basal part comparatively smaller and the corniform 

 processes somewhat differing in shape; terminal part rather large, subtriangular. 



Colour of shell whitish pellucid. 



Length of adult female 0.70 mm. 



Remarks. The present form is at once recognised from any of the other 

 known species by the enormous development of the alaeform expansions of 

 the valves, giving the animal a quite particular appearance, and rendering it 

 rather difficult to get a lateral view of the shell. 



Occurrence. The species was first observed in the upper part of the 

 Christiania Fjord, where a few specimens were taken in a depth of about 30 

 fathoms, and I have subsequently met with it occasionally also in some other 

 places on the south coast of Norway (Ris0r, Korshavn) at about the same depth. 



Distribution. British Isles, Shetland. 



?8 Crustacea. 



