160 



POST-TERTIARY ENTOMOSTRACA. 



26. Cythere concinna, Jones. Plate IV, figs. 1 — 16. 



1856. Cythere concinna, Jones. Monog. Tert. Entom., p. 29, pi. iv, figs. 7 a — 7f. 

 186.5. Cythereis clavata, G. O. Sars. Overs. Norg. mar. Ostrac, p. 39. 

 1868. Cythere concinna, Brady. Monog. Rec. Brit. Ostrac, p. 408, pi. xxvi, 



figs. 28 — 33, and pi. -xxxviii, fig. 7. 



Carapace of the female, as seen from the side, oblong, subquadrangular, highest in. 

 front of the middle, greatest lieight equal to more than half the length ; anterior 

 extremity broadly rounded ; posterior narrowed, obliquely subtruncate, sometimes 

 emarginate in the middle (figs. 1, 5, 12), at others simple (fig. 6) or angularly produced 

 (fig. 7) ; superior margin gibbous or prominently angular in front of the middle, thence 

 sloping backwards with an irregularly curved or sinuous line ; inferior margin straight or 

 slightly sinuous. Outline, as seen from above, oblong-ovate, greatest width in the 

 middle and equal to half the length ; extremities obtuse, broad and nearly equal ; 

 lateral margins irregularly sinuous. End-view subpentagonal ; height greater than the 

 width. The carapace of the male is, as usual, considerably narrower and more 

 elongated. The surface of the shell is subject to much variation in its sculpture. 



The specimens represented at figs. 9 and 11 belong to the most strongly sculptured 

 class, and exhibit the peculiar markings of the species with great distinctness; these 

 consist of a prominent ridge running parallel to and a little within the anterior margin, 

 and continued along the ventral border to the hinder end of the valve, a large rounded 

 eminence a little below and in front of the centre of the valve and a flexuous rib running 

 from the posterior margin of this tubercle towards the supero»posteal angle ; the rest of 

 the shell-surface is marked with small closely set puncta, and with minor ribs radiating 

 from the larger ridges and tubercles ; the posterior portion of the shell is also sometimes 

 marked with distinct angular recticulations, as in fig. 9. Sometimes, however, the 

 shell-scul[)ture is very feebly developed (fig. 6), the tubercles and ridges being very 

 faintly indicated, the general surface obscurely pitted, and bearing a few short rigid 

 hairs. Hinge-processes strongly developed. 

 Length, ^sth of an inch. 



Between the simplest and the most elaborately sculptured forms all shades of 

 variation may be found, and we have not been able to detect any constant relation between 

 the varieties of sculpture and the geological position or other conditions of life ; the most 

 ornate and the most simple forms are found living in our own seas almost side by 

 side, and have apparently existed in a similar manner in the seas of the Glacial Epoch. 

 Various stages of growth are represented in figs. 13 — 16. C. concinna has been found 

 in the recent state in the Arctic Sea, and on the coasts of Norway, Canada, Scotland, and 

 north of England ; its range of depth appears to be from ten to sixty fathoms. 



