454 Jones and Sherhorn — Tertiary Entomostraca. 



41. Ctthereis Pkkstwichiana, sp. nov. PI. XL Figs. 11a, lift. ' 



A very small neat Cythereis, with well-developed marginal rim 

 in front, which, passing along the ventral region, gradually rises 

 higher, and ends in a sharp rectangle. A similar, but lower, ridge 

 follows the dorsal edge. Both are more or less crenulated. There 

 is a central boss, and a short ridge behind it, ending, like the others, 

 at the sudden posterior slope, which terminates in a narrow, produced, 

 flat, and toothed edge. The surface of the valve is somewhat 

 depressed, and is covered with a distinct lace-like reticulation. 

 Edge- view, subsagittate. 



This form is clearly related to that figured in the " Monogr. Cre- 

 taceous Entom.," 1849, pi. v. fig. 13b., which we propose to remove 

 from C. ornatissima (Geol. Mag., 1870, p. 75). We now have closely 

 allied forms from the Chalk of other localities of the British Islands, 

 and the distinctness of this new species, named after Prof. Prest-. 

 wich, becomes more and more apparent. 



Two valves from the London Clay of Whitecliff Bay, Isle of 

 Wight. Collected by C. D. Sherborn. 



42. Cythereis Hoernesi, Speyer. 



Gytherella Soernesi, Speyer. Ostrac. Cassel. Tertiar., 1863, p. 32, pi. iii. fig. 7 ; 

 pi. iv. fig. 1. 



Oblong ; swollen into a distinct boss in the centre ; ends round, 

 the front margin semicircular and deeply fenestrated, the hind 

 margin depressed and slightly toothed. Surface reticulated, orna- 

 mented with two prominent ridges, the dorsal and most striking of 

 which, strong, fenestrated, and somewhat convex, partly obscures 

 the hinge-line, and curves forwards and downwards below the front 

 hinge. The ventral ridge is not so strong ; both are sharply angular 

 posteriorly. 



The only marked difference between our specimen and that figured 

 by Dr. Speyer is — that the dorsal ridge in the former is much better 

 developed, being higher, thinner, fenestrate, more delicate, and 

 ending posteriorly in a much sharper angle. 



A single valve from the White (Coralline) Crag. T. E. Jones' 

 Collection. 



43. Cythereis corrugata (Eeuss), var. 



This valve is rugosely reticulate, with the longitudinal meshes 

 stronger and more persistent than the transverse. Several allies of 

 this form are figured in plates xxi. and xxii. of the "Keport 

 Challenger Ostracod.," 1880. Of the previously published forms we 

 find that C. corrugata, Eeuss, Haidinger's Nat. Abth. vol. iii. p. 79, 

 pi. X. fig. 14, is the nearest to ours, although it varies in being 

 squarer, stronger, swollen at centre, and strongly rimmed on the 

 front margin. 



One specimen, collected by the late F. Edwards from the Fluvio- 

 marine beds, Headon, Isle of Wight. British Museum. 



44. Cythereis cornuta (Eoemer). 

 Three or four specimens of this form from Bracklesham, of which 



