226 



119. Cytheropteron hamatum, G. O. Sars. 



(PI. CIV, fig. 2). 

 Cytheropteron hamatum, G. O. Sars, Chr. Vid. Selsk. Forhandl. 1369, p. 172. 



Specific Characters. Female. Shell much shorter and stouter than in the 

 preceding species, with the alaeform expansions far less developed, seen later- 

 ally, irregularly oval in shape, g eatest height in the middle and about equal 

 to 3 /5 of the length, dorsal margin considerably arched, ventral slightly sinuated 

 in front and evenly convex behind, anterior extremity rather obliquely rounded, 

 posterior produced in the middle to a well defined protuberane, narrowly 

 truncated at the end; seen dorsally, somewhat lozenge-shaped, with the greatest 

 width (between the tips of the alaeform expansions) not nearly attaining the 

 length, both extremities sharply pointed, the posterior more abruptly contracted 

 than the anterior. Valves somewhat coarser than in the preceding species, 

 with the alaeform expansions short rectangular in shape and issuing rather 

 behind the middle, each produced at the end to a sharp spiniform process 

 more or less distinctly curved forwards in a hamiform manner; surface marked 

 with slight pittings arranged partly in concentric rows. Antennae comparatively 

 less slender than in C. alatum, but of a very similar structure. Legs likewise 

 less narrow and prolonged than in that species. 



Male resembling the female in the shape of the shell, butt of somewhat 

 smaller size. Copulative appendages rather like those in the preceding species, 

 differing however somewhat in the shape of the corniform processes, as also 

 in that of the terminal part, which is narrowly rounded at the end. 



Colour of shell whitish grey. 



Length of adult female 0.62 mm. 



Remarks. Though rather closely allied to C. alatum, this species is at 

 once d'stinguished by the more compact appearance of the shell and by the 

 far less prominent alaeform expansions, wh ch do not exhibit any appendages 

 posteriorly and have the terminal spine somewhat hamiform curved, hence the 

 specific name proposed. 



Occurrence. The only locality where 1 have as yet met with this species, 

 is at Skraaven, one of the Lofoten islands. It was found here occasionally at 

 the considerable depth of 120300 fathoms, muddy bottom. Norman ha 

 however taken it at Stoksund, west coast of Norway. 



Distribution. Spitzbergen, Dawis Strait. 



Fossil. Scotland. 



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