180 POST-TERTIARY ENTOMOSTRACA. 



creniilated, consisting of two not very prominent terminal projections of the right which 

 articulate with corresponding sulci of the left valve. Male unknown. 

 Length, g^tli of an inch. 



Cytheridea lacustris is an inhabitant of fresh water. It appears to be of rare 

 occurrence in the living state, having been noticed only in two localities in Scotland and 

 one in England and in some Norwegian lakes. The tubercular eminences of the shell 

 are very variable in number and degree of elevation, sometimes being almost obsolete, 

 and at others forming a very conspicuous feature. The generic position of the species 

 must be looked upon as provisional until the male has been seen and examined in the 

 recent state. 



Distribution. Recent, — Norway, Scotland, England. 



Fossil. — England : Hornsea, Branston Pen. Scotland : Crofthead, Dipple. 



5. Cytheridea Sorbyana, Jones. Plate VII, figs. 7 — 12. 



1856. Cytheridea Soebyana, Jones. Monog. Tert. Entom., p. 44, pi. iv, figs. 



6 a — 6 e. 

 1865. — DENTATA, G, 0. Sars. Overs. Norg. mar. Ostrac. (right valve), 



p. 56. 

 1865. — iNEKMis, G. O. Sars. Overs. Norg. mar. Ostrac. (left valve), 



p. 5G. 

 1868. — Sorbyana, Brady. Monog. Rec. Brit. Ostrac, p. 428, pi. xxix, 



figs. 1 — 6. 



Carapace, as seen from the side, broadly subtriangular, greatest height situated in 

 front of the middle and equal to about two thirds of the length ; anterior extremity 

 broadly rounded and bearing several (6 — 8) triangular spines, which point obliquely 

 downwards and forwards; posterior extremity narrow and somewhat exserted below; 

 superior margin much elevated and almost gibbous over the anterior hinge, thence 

 sloping in a continuous and bold curve to the postero-ventral angle ; inferior margin 

 almost straight, terminated behind by a single stout pointed spine, which projects 

 obliquely downwards and backwards from the extremity of the right valve. The left 

 valve is higher than the right, the spines on its anterior margin are often almost obsolete, 

 and its posterior angle is rounded off and bears no spine. Outline, as seen from above, 

 broadly oval, greatest width in the middle and equal to more than half the length, 

 raucronate in front. Surface of the shell marked, except toward the centre, with coarse, 

 irregularly sinuous, concentric furrows, and pitted, usually in the interspaces, with 

 numerous minute punctures. 



Length, ^th of an inch. 



