36 



CHESTER OSTRACODES OF ILLINOIS 



Cavellina congruens Cooper, n. sp. 

 Plate 5, figures 20-21 



Carapace elliptical, ends equally rounded ; 

 dorsum slightly more curved than venter; 

 overlap around entire margin, greatest along 

 the venter, resulting in trough-like furrow 

 in mid-portion; hinge straight; sides 

 smoothly convex, greatest thickness just 

 hack of middle ; greatest length and height 

 central. 



Length, 1.10 mm; height, 0.51 mm; 

 thickness, 0.35 mm. 



Clore formation, locality 4, abundant. 



This species is distinguished by its sym- 

 metry and by the unusual overlap along 

 the venter. 



Cavellina dispar Cooper, n. sp. 

 Plate 5, figures 28-29 



Carapace subelliptical ; dorsal margin 

 slightly more arched than ventral ; ends 

 asymmetrically rounded, making greatest 

 length above middle ; overlap greatest 

 around dorsal and posterior margins; hinge 

 slightly sinuous; in dorsal view left valve 

 appears much shorter than right because of 

 offset at articulation ; greatest thickness 

 near but somewhat back of middle ; greatest 

 height central. 



Length, 0.82 mm; height, 0.49 mm; 

 thickness, 0.31 mm. 



Menard formation, locality 20, common. 



C. dispar may be distinguished by its 

 peculiar overlap, and by the differences in 

 length of the two valves. 



Cavellina geisi (Croneis and Gale) 



Plate 5, figures 43-44 



Cythcrella geisi Croneis and Gale, 1938, Denison 

 Univ. Bull., Jour. Sci. Lab., vol. 33, p. 291, 

 pi. 5, fig. 32, Golconda formation. 



Length, 0.93 mm; height, 0.58 mm; 

 thickness, 0.38 mm. 



Vienna formation, locality 10, common. 



This Vienna Cavellina agrees closely 

 with the figure and description of the Gol- 

 conda form of Croneis and Gale. In addi- 

 tion this specimen shows, in dorsal v'ltw, a 

 somewhat sinuous hinge line and the in- 

 ternal ridge in the posterior quarter is 

 suggested by a faint interruption of the re- 

 gular convexity of the valves at this point. 



Cavellina glandella (Whitfield) 



Plate 5, figures 49-50 



Cytherellina glandella Whitfield, 1882, Am. Mus. 

 Nat. Hist., Bull. 3, vol. 1, p. 54, pi. 9, figs. 

 28, 29, Spergen limestone. Hall, 1882, In- 

 diana Dept. Geol. Nat. Res., 12th Ann. Rept, 



pi. 32, figs. 28, 29, Spergen limestone. 



Cummings and Beede, 1905, ibid., 30th Ann. 

 Rept., pi. 26, figs. 28, 29, Spergen limestone. 



Cytherella glandella. Girty, 1915, U. S. Geol. Sur- 

 vey, Bull. 593, p. 136, Batesville sandstone. 



Cavellina glandella. Geis, 1932, Jour. Paleon- 

 tology, vol. 6, p. 186, pi. 26, figs. 9a-d, Salem 

 limestone. 



Length, 1.0 mm; height, 0.60 mm; 

 thickness, 0.29 mm. 



Kinkaid formation, locality 3, common. 



These Chester specimens, although smaller 

 than those described from the Salem, appear 

 to be identical in form ratio and other 

 structural features. 



Cavellina exila Cooper, n. sp. 

 Plate 5, figures 34-36 



Carapace long, thin ; dorsal and ventral 

 margins almost straight, subparallel ; over- 

 lap moderate; anterior end uniformly 

 rounded ; postero-ventral margin almost 

 straight, posterior end not smoothly curved, 

 greatest length above middle; greatest 

 height and thickness posterior ; hinge sinu- 

 ous, sharply curved in middle of anterior 

 half, produced by pronounced overlap at 

 this point. 



Length, 1.27 mm; height, 0.67 mm; 

 thickness, 0.28 mm. 



Renault formation, locality 13, rare; 

 Vienna formation, locality 10, common; 

 Menard formation, locality 7, common; 

 Clore formation, locality 26, common. 



Cavellina librata Cooper, n. sp. 

 Plate 5, figures 37-38 



Carapace subelliptical; dorsum rounded 

 or broadly arched, venter straight ; overlap 

 around entire margin, most pronounced on 

 dorsum ; in dorsal view posterior end bound- 

 ed by almost straight sides, giving somewhat 

 pointed appearance ; anterior end sharply 

 rounded ; hinge almost straight. 



Length, 0.78 mm; height, 0.45 mm; 

 thickness, 0.29 mm. 



Clore formation, locality 4, common. 



Cavellina longula Cooper, n. sp. 

 Plate 5, figures 41-42 



Carapace elongate ; dorsum arched, vent- 

 er almost straight ; left valve considerably 



