14 
THE ENTOMOSTRACA OF 
Subgenus CytJiereis, nobis. 
Synonyms. Cythere, Munster. 1830. Jahrbucli fiir Mineralogie, &c. 
Cytherina, Rcemer, 1838. Jahrbucli fiir Miiieralogie, &c. 
— — 1840. Verstein. Kreidberg. 
— - Reim. 1845. Verstein. Bdbm. Kreideform. 
Cythere, Cornuel. 1846. Mem. Geol. Soc. France. 
Cytherina, Williamson. 1847. Transact. Manchester. 
Cypridina, Bosquet. 1847. Mem. Soc. Royale Li^ge. 
The carapace-valves of Cythereis have an almost regularly oblong shape. The 
superior (dorsal) and inferior (ventral) borders of the valves lie nearly parallel to each 
other ; the superior border, however, especially in the left (larger) valve, trends up- 
wards as it approaches its anterior extremity, making at its junction with the anterior 
border a more acute angle than that formed by the junction of the anterior and 
ventral borders, and thereby leaving a greater space between the anterior hinge 
and the ventral margin, than between the same margin and the posterior hinge. The 
middle of the inferior border is slightly incurved. The anterior border is nearly 
semicircular, it is trenchant and bevilled off inwardly ; its superior moiety is more or 
less compressed, and, as it were, drawn back to meet the dorsal border. The anterior 
third of the carapace-valves is always depressed. The posterior border is shorter 
than the anterior ; it is more or less acute, its ventral moiety forming the segment of 
a circle, and the edge of its superior moiety suddenly returning in a straight or sinuous 
line to meet the dorsal border. This somewhat triangular extremity, occupying some- 
times a fourth of the valve, is much below the level of the rest of the surface, being 
suddenly and strongly depressed. The inferior or ventral moieties of the anterior 
and posterior borders are always furnished with spines, and sometimes nearly the 
whole of the anterior border. 
The dorsal half of the valve, or that superior to the median line, has always less 
convexity than the ventral or inferior half, which latter is frequently very strongly 
raised, taking an angular form, with the ventral surface of the valve at a right angle 
to its lateral surface ; and as the ventral half of each valve gradually increases in 
thickness, as it recedes from the anterior extremity until it is abruptly terminated 
nearly opposite to the posterior hinge, the ventral aspeet of the carapace is flat, and 
more or less of a triangular or sagittiform shape, varying, indeed, from an irregular 
oblong more or less elongate to a triangle, the posterior angles of which are sometimes 
far apart, and giving origin to Dr. Reuss’s group of “ CormtosT The dorsal aspect, 
on the contrary, is not flat, but angular or culminate, narrow in front, and increasing 
in wddth backwards towards the ventral keels. For the same reasons the anterior 
aspect of the carapace is generally triangular, acute superiorly, and inferiorly more or 
less extended. 
