198 



97. Cythereis mucronata, G. O. Sars. 



(PI. XCIl.) 



Cythereis mucronata, G. O. Sars, Oversigt af Norges marine Ostracoder, p. 48. 

 Syn: Cy there spinosissima, Brady. 



Specific Characters. Female. Shell of an appearance rather similar to 

 that in the preceding species, though comparatively somewhat more elongate; 

 seen laterally, oblong quadrangular in shape, with the greatest height in front 

 and but very little exceeding half the length, dorsal margin straight or slightly 

 concaved, sloping gently towards the rather prominent supero-posteal corner, 

 ventral margin distinctly convex in its anterior part, anterior extremity broadly 

 rounded, posterior much narrower and obtusely truncated, with the lower corner 

 rounded off; seen dorsally, pronouncedly lozenge-shaped, the side-edges being 

 angularly bent behind the middle, both extremities somewhat blunt at the ends. 

 Valves of firmer consistency than in C. Jonesi and quite opacous, each exhibiting 

 laterally, near the ventral face, a well-marked wing-like expansion terminating 

 in a strong sharply pointed spiniform process, and bordered with a regular 

 row of somewhat spatulate spines continued for some distance upwards along 

 the anterior extremity, frontal edges of the valves, as in the preceding species, 

 provided above with a thin undivided crest terminating just above the eye- 

 tubercle in i sharp corner, lower part of the edges bordered with a regular 

 series of densely set strong denticles; posterior edges armed with 68 somewhat 

 unequal spines, the lowermost particularly strong and sharply pointed. Lateral 

 faces of the valves rough from numerous somewhat irregular, more or less 

 sqamiform prominences, those nearest the dorsal margin of each valve being 

 however of a more uniform appearance and arranged in a regular longitudinal 

 row. Eye-tubercles well marked, though somewhat smaller than in C. Jonesi. 

 Structure of the several limbs very similar to that in the said species. 



Male slightly larger than female, and having the shell somewhat more 

 elongate in shape. Legs exactly as in female, the 2nd pair not being trans- 

 formed. Copulative appendages only slightly differing from those in the 

 preceding species, basal part however more triangular in shape, und terminal 

 part obtusely produced behind. 



Youngs, recently hatched, as in the preceding species, with the spines 

 bordering the anterior edges and the lateral expansions of the valves replaced by 

 undivided thin marginal lamellae, the expansions being however less producec 

 than in the youngs of C. Jonesi. 



Colour of shell dark fuscous. 



Length of adult female 1.10 mm. 



