32 TERTIARY ENTOMOSTRACA OF ENGLAND. 



Sppciraens numerous, from the Ehivio-marine bods of Headon, Tsle of Wight. 

 (F. B. Edwards' Collection in the British Museum.) 



XII. CYTHEREIS, /on(!s, 1849. 



Monogr. Cretac. Entom., 1819 (subgenus), p. 14 ; Monogr. Tert. Entom., 1857, p. 37. 



This quasi-generic form is conveniently kept apart on account of its easily 

 recognisable valves. In the several species defined as belonging to Gythereis by 

 G. 0. Sars, the anatomical structure is not very different from that of Gi/there, 

 and the valves are in many cases like those of Gythere} In other cases the valves 

 are subquadrate, angular, and rough, and these are usefully separated, not as a 

 natural, but as an artificial group, convenient for collectors and others. 



1. Gythereis coeeugata (Reuss). Var. not). Plate III, figs. 19 a, b. 



Cttheeeis cobeuoata (Reuss). Jones if Sherborn, Geol. Mag., 1887, p. 454. 



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 ' Report Challenger Ostracod.,' 1880. Of the previously 

 published forms we find that G. corrugata, Reuss, ' Haidinger's Nat. Abth.,' 

 vol. iii, p. 79, pi. X, fig. 14, is the nearest to ours, although it difi'ers in being 

 squarer, stronger, swollen at centre, and strongly rimmed on the fi-ont margin. 



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

 beds, Headon, Isle of Wight, is in the British Museum. 



2. Cttheeeis senilis, Jones, 1857, from the Crag, takes its place here. (Brit. Mus.) 



3. Gythereis Hoernesi {Speijer). Plate I, fig. 7. 



Cttheee Hoeenest, Speyer. Ostrac. Cassel. Tertiar.,^ 1863, p. 32, pi. iii, fig. 7 ; 



pi. iv, fig. 1. 

 Cttheeeis — Jones & Sherhorn. Geol. Mag., 1887, p. 454. 



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

 semicircular and deeply fenestrated, the hind margin depressed and slightly 



' See Dr. G. S. Brady's remarks, ' Trans. Linn. Soc.,' vol. xxvi, pp. 395 and 401. 

 2 'Berichl Ver. Naturkuude Cassel,' 1860-62 (1863). 



