56 



CHESTER OSTRACODES OF ILLINOIS 



The large number of reversed forms of 

 Sousabella which have been discovered in the 

 Chester series has shown the fallacy of try- 

 ing to determine generic classification by 

 overlap alone. Overlap, inseparably tied up 

 with orientation, has been the subject of 

 much discussion in recent ostracode litera- 

 ture, and it has shown that, in every de- 

 scription, most careful consideration must be 

 given to these features. Since the hinge 

 serves a most important physiological need, 

 it seems advisable to consider variations in 

 this feature of sufficient importance to mark 

 generic if not greater differences in shell 

 taxonomy. 



It is apparent therefore that Jonesina be- 

 comes a very restricted genus if all species 

 with the channeled hinge line are removed 

 to Sansabella or to Sansabella-like genera. 

 An emended description of Jonesina, con- 

 sidering all points raised by recent workers, 

 follows : 



Carapace ovate, somewhat elongate, thin 

 to obese, greatest thickness posterior ; 

 varies in lateral outline from subelliptical 

 to an approximate parallelogram ; valves 

 unequal; overlap around entire free margin 

 usually prominent ; variously lobed ; hinge 

 straight, obscurely cardine, about two-thirds 

 as long as total length of shell; median 

 sulcus opening into cardinal area, usually 

 deep and elongate, before which occur one 

 or more fairly well-defined lobes ; surface 

 smooth or reticulate. 



The obesity of the posterior half of the 

 carapace may produce a short canoe-shaped 

 channel at the hinge line, but this is not to 

 be confused with the straight V-shaped chan- 

 nel running the entire length of the sansa- 

 belloid hinge, nor is the obscure rounded 

 notch present, as at each end of the hinge 

 of Sansabella. 



Jonesina craterigera (Brady) 

 Plate 11, figures 36-39 



Beyrichia craterigera (Brady ms.) Jones, 1886, 

 Geol. Mag. n. s., dec. 3, vol. 3, p. 439, pi. 12, 

 figs. 7a, b, Carboniferous of Great Britain. 



Jonesina craterigera. Ulrich and Bassler, 1908, 

 Proc. U. S. Nat. Mus., vol. 35, p. 324, pi. 44, 

 figs. 13, 14.— ? Harlton, 1927, Jour. Paleon- 

 tology, vol. 1, p. 203, pi. 32, figs. 5a, b, 

 Lower Glenn formation. 



Female: length, 1.0 mm; height, 0.53 

 mm; thickness, 0.49 mm. 



Male: length, 0.75 mm; height, 0.40 

 mm ; thickness, 0.33 mm. 



Golconda formation, locality 19, rare; 

 Glen Dean formation, locality 1, rare. 



Plate 11 shows two specimens, identical 

 in lateral view, but the one from the 

 Golconda is considerably thicker near the 

 posterior end, whereas the Glen Dean form 

 is thickest near the center of the shell. The 

 specimen figured by Harlton lacks the 

 postero-ventral truncation of the Mississip- 

 pian form. 



Jonesina equilatera Cooper, n. sp. 

 Plate 11, figures 15-16 



Carapace ovate, with parallel dorsum and 

 venter ; hinge straight, venter slightly con- 

 vex ; ends equal in height and curvature ; 

 sinus procentral, narrow at bottom, widen- 

 ing toward dorsal area; overlap prominent, 

 especially along venter ; surface smooth. 



Length, 1.0 mm; height, 0.60 mm; 

 thickness, 0.36 mm. 



Paint Creek formation, locality 2, com- 

 mon. 



/. equilatera is distinguished by its al- 

 most symmetrical outline and by its thin- 

 ness. 



Jonesina intermedia Croneis and Bristol 

 Plate 12, figures 8-9 



Jonesina interjnedia Croneis and Bristol, 1939, 

 Bull. Denison Univ., Jour. Sci. Lab., vol. 34, 

 p. 75, pi. 3, figs. 10-11, Menard formation. 



Length, 0.64 mm; height, 0.39 mm; 

 thickness, 0.27 mm. 



Vienna formation, locality 36, rare. 



Jonesina puncta Morey 



Plate 12, figures 20-21 



Jonesina? puncta Morey, 1935, Jour. Paleontol- 

 ogy, vol. 9, p. 476, pi. 54, fig. 1, Amsden 

 formation. — Coryell and Johnson, 1939, ibid., 

 vol. 13, p. 214, pi. 26, fig. 3, Clore formation. 



Jonesina consimilis Croneis and Bristol, 1939, Bull. 

 Denison Univ., Jour. Sci. Lab., vol. 34, p. 74, 

 pi. 3, figs. 29, 30, Menard formation. 



Kloedenella sigurdi Coryell and Johnson, 1939, 

 Jour. Paleontology, vol. 13, p. 215, pi. 26, 

 fig. 2, Clore formation. 



Nuferella ivellsi Coryell and Sohn, 1938, Jour. 

 Paleontology, vol. 12, p. 602, pi. 69, fig. 9, 

 Reynolds limestone. ' 



Length, 0.73 mm; height, 0.44 mm; 

 thickness, 0.29 mm. 



Clore formation, locality 26, rare. 



