28 THE ENTOMOSTRACA OE 



Sub-genus Cytherella, nobis. 



Cythere, Miinster. 1830. Jahrbucli f. Min. 



CyTHERiNA, Lyell and Lonsdale. 1838. Elements of Geology. 



— Rcemer. 1838. Jahrbuch f. Min. 



— — 1840. Verstein. Norddeutscli. Kreid. 



— Reicss. 1845. Verstein. Bolim. Kreid. 

 Cythere, Cornuel. 1846. Mem. See. Geol. France. 

 Cytheeina, Williamson. 1847. Transact. Manchest. 



— and Ci'PRiDiNA, Bosquet. 1847. Mem. Soc. Eoy. Liege, 



8ub-c/eneric characters. — In this peculiarly distinct group the carapace -valves are 

 oblong, and vary in the convexity and smoothness of the surface. The right valve is 

 larger than the left, and its contact-margin thicker than that of the opposite valve. 

 A groove, excavated along the inner edge of the contact-margin of the right valve, 

 receives a narrow trenchant ridge or flange, which runs along the inner edge of the 

 contact margin of the left valve. The outer edge of the groove of the anterior margin 

 is itself sometimes produced into a slight ridge, which in the closed carapace lies 

 outside the flange of the opposite valve. The outer part of the contact-margin of the 

 left valve lies against, but does not wholly cover, especially on the posterior and dorsal 

 borders, the salient outer half of the contact-margin of the right valve ; the margin of 

 the \?iX^&c^^vQ projecting beyond, but not overlapping, the smaller valve. The substance 

 of the shell of Cytlierella is somewhat greater in the posterior than in the anterior parts 

 of both valves, the thickness gradually increasing from before backwards ; so that in 

 the large valve the groove on the anterior margin is slight, and accompanied by a 

 narrow outer boundary, whilst posteriorly the salient part of the contact-margin is 

 broader than the groove. From the same cause the flange of the lesser valve occupies 

 nearly the whole thickness of the anterior margin, although at this part it is thin and 

 low ; whilst it gradually increases in size towards the posterior extremity, where it is 

 strongly marked, and where the accompanying boundary of contact-margm is as broad 

 as the base of the ridge. The valves of Cytlierella (as previously mentioned) exhibit 

 a small round tubercle on their inner surface between the centre and the dorsal margin, 

 which is faintly marked in the young shell, and increases in size with the age of the, 

 individual. 



No. 1. Cytherella ovata, Bcemer. Tab. VII, fig. 24 a — i. 



Cytherina, Lyell ajid Lonsdale. 1838. Elem. Geolog. p. 55, (woodcut) fig. 19. 



— OVATA, Roetner. 1840. Verstein. Kreid. p. 104, n. 4, pi. xvi, fig. 21. 



— — Reuss. 1845. Verstein. Bohm. Kreid., p. 16, n. 6, pi. v, fig. 35. 

 Cythere amygdaloides, var. brevis, Cornuel. 1846. Mem. Soc. Geol. de France, 



ser. sec, torn, i, part. 2, p. 199, pi. viii, fig. 12. 

 Cytherina reniformis. Bosquet. 1847. Ent. foss. Maestricht, p. 6, n. 1, pi. i, fig. ' a—f. 



— L^vis, Williamson. 1847. Trans. Manchest. Phil. Soc. 1847, pi. iv, fig. 80. 



