223 



Gen. 44. Cytheropteron, G. O. Sars, 1865. 



Generic Characters. Shell of somewhat varying shape, generally thin and 

 pellucid, with no sharply marked sculpture. Valves slightly unequal, each 

 provided with a well defined, more or less prominent alaeform lateral expansion 

 occurring near the ventral face. Hinge imperfectly developed. Eyes wholly 

 absent. Anterior antennae with the terminal part, as a rule, only composed of 

 3 joints clothed with scattered simple setae, last joint very small. Posterior 

 antennae with a well marked dividing suture of the penultimate joint, and with 

 the anterior setiierous ledge of this joint located far below. Mandibles strongly 

 dentate at the end, palp of moderate size, but with the vibratory plate con- 

 siderably reduced, being only provided with a single seta. Maxillae with the 

 masticatory lobes rather produced, palp very narrow, with the distal joint small, 

 vibratory plate, as in Cytherura, provided at the base with 2 thin abruptly 

 deflexed setae issuing from a well defined lobule. Legs more or less slender 

 and prolonged. Posterior end of body drawn out to a much prolonged conical 

 point. Caudal lamellae short, with 3 small bristles, one apical and 2 lateral. 

 Copulative appendages of male without any freely projecting string insides, but 

 provided below with 3 peculiar corniform processes, the foremost more or less 

 ramified at the end; terminal part simple, lamellar. 



Remarks. The present genus is chiefly characterised by the peculiar alae- 

 form lateral expansions of the valves, to which indeed the generic name pro- 

 posed alludes. It differs moreover from the preceding genus in the wholly 

 absence of eyes, as also somewhat in the structure of the antennae. G. W. 

 Muller considers it to be nearly allied to Cytherura, but I think that its relation- 

 ship to Loxoconcha is rather closer. Several species of this genus have been 

 recorded, all of them being true deep-water forms. In the following pages 10 

 species will be described as members of the Norwegian Fauna. 



117. Cytheropteron latissimum, (Norman). 

 (Pi. cm). 



Cythere latissima, Norman, Nat. Hist. Trans. Northumb. & Durham, Vol. I, p. 19, 



PI. VI, figs. 5-8. 



Syn: Cytheropteron convexum, G. O. Sars. 



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

 expansions only slightly prominent, seen laterally, oval subtriangular in shape, 

 somewhat higher in front than behind, greatest height about equal to 3 /5 of 



