48 THE ENTOMOSTRACA OF 



No. 3. Cytherideis unisulcata, Jones. Plate TV, fig. 10. 



Cytherideis unisulcata, Jones. Memoirs Geol. Survey, 1856, p. 157, t. 7, fig. 23. 



INCH. 



Length, -^ Upper Eocene : Isle of Wight. 



Valve triangular, broadest anteriorly, convex, impressed across the middle by a 

 transverse furrow. 



The only specimen that I have met with is very small and not well preserved : its 

 characters, however, are sufficiently distinct for notice. 



It occurs with Candona Forbesii in the green shales of the Osborne series, at Cliff 

 End, Colwell Bay, Isle of Wight. 



No. 4. Cytherideis unicornis, Jones. 



Cytherideis unicornis, Jones. Memoirs Geol. Survey, 1856, p. 158 t. 7, fig. 24 — 26. 



inch. 

 Length, -Jj Upper Eocene : Isle of Wight. 



Valves thick, sub-triangular in the young state, almost oblong when adult, broadest 

 and most depressed anteriorly. Young individuals are impressed on the middle of the 

 dorsal portion of each valve with two more or less distinct transverse furrows, the 

 posterior of which is the largest and most constant. The anterior furrow is shorter 

 and more oblique than the other, and often runs into it, forming a Y-like impression. The 

 furrows are associated with several irregular tubercles, of slight elevation, one of which, 

 placed behind the chief furrow, is persistent, and increases in size, whilst the others 

 disappear as the animal grows older and the carapace enlarges. The furrows also 

 gradually disappear with the advanced growth of the animal, until a single, slightly 

 recurved spine, or pointed tubercle, remains on the postero-dorsal third of each valve- 

 The surface of the valves is faintly and irregularly punctate. 



Dorsal aspect narrow-acute-oval, modified by the lateral spines. 



This interesting species has much of the general character of the oblong and tuber- 

 cled Cyprideis (page 21) ; but it wants the knurled hinge-teeth of the latter sub-genus. 



Cythere {Cytherideis) unicornis is very plentiful in a crushed state between the 

 laminae of a dark-grey marl of the Hempstead series, at Hempstead Cliff, Isle of 

 Wight. The specimens were submitted to me, and have been described for the 

 Geological Survey, whilst this Monograph was in progress, and since the plates were 

 finished. 



