37 



7. Polycopsis compressa (Brady & Robertson). 



(PI. XVII, fig. 2) 



Poly cope compressa, Brady & Robertson, Ann. Mag. Nat. Hist. ser. IV, Vol. Ill, p. 20, 



PI. XXI, figs. 511. 



Specific Characters. Female. Shell rather compressed, seen laterally, of 

 a somewhat obliquely rounded shape, greatest height in the middle and only 

 little inferior to the length, dorsal and ventral margins evenly curved, anterior 

 extremity broadly rounded and only very slightly bowed in the middle, posterior 

 narrower and quite evenly rounded at the end, without any trace of an angle 

 above; seen dorsally, narrow oblong in outline, with the lateral edges nearly 

 straight in the middle, greatest width somewhat behind the middle and not 

 nearly attaining half the length, anterior extremity more narrowed than the 

 posterior. Surface of valves smooth, of a dull appearance, not exhibiting any 

 obvious sculpture; anterior part of the ventral edges with about 16 well-marked 

 serratures, smaller however than in P. serrata. Anterior antennae with both 

 lappets of the 2nd joint well defined, the proximal one however much narrower 

 than the distal one, both tipped with a single seta; 2 other well-developed 

 ciliated setae, not found in Polycope, present, the one issuing from the upper 

 distal corner of the 1st joint, the other on the posterior edge of the 2nd joint 

 near its end; terminal part of the antenna distinctly 4-articulate and tipped 

 with 5 natatory setae. Caudal lamellae each armed, as in Polycope, with 7 claws, 

 intercurrent processes of the margin comparatively small. 



Colour opaque whitish. 



Length of the specimen examined 0.61 mm. 



Remarks. This form was at first described by Brady and Robertson as 

 a species of the genus Polycope, but was subsequently by G. W. Miiller justly 

 removed as the type of a distinct genus. The latter author had also an oppor- 

 tunity of examining male specimens, and has stated the presence in them of 

 a well-developed apical claw on the inner ramus of the posterior antennae, a 

 feature not found in the species of Polycope. The present form may, also 

 without dissection, be easily recognised from any of the species of that genus 

 described in the preceding pages, by the much more compressed shell and by 

 the rather conspicuous serratures of the anterior part of the ventral edges. 



Occurrence. A solitary female specimen only of this form has as yet come 

 under my notice. It was taken at Korshavn, south coast of Norway in com- 

 paratively shallow water. 



Distribution. British Isles (Brady), Mediterranean (G. W. Muller). 



