ACRONOTELLIDAE 



23 



SYSTEMATIC DESCRIPTION 



Three hundred and twenty-five species 

 and one variety of ostracodes have been 

 identified from the Chester series in Illinois, 

 126 of which are newly described in this 

 report. All but 38 species and one variety 

 of the previously described forms are repre- 

 sented in our collections. Descriptions of 

 the new species are presented in the follow- 

 ing pages together with redescriptions of 37 

 species known from other areas (including 

 two from western Kentucky) which have 

 been recognized in Illinois for the first time. 

 In addition descriptions of two species from 

 the Fayetteville shale, one of them new, and 

 two species from the Reynolds formation 

 of the Mauch Chunk series are included 

 for purposes of comparison. One new sub- 

 family and 10 new genera are proposed. 



Illustrated on the plates are all of the new 

 species, 117 species described by Croneis and 

 associates and by Coryell and Johnson that 

 are present in our collections, and 45 species 

 described from other areas, all but four of 

 which are known in Illinois. 



The dimensions listed in the following 

 descriptions refer to the holotypes of new 

 species and the principal figured specimens 

 of others. 



Family Acronotellidae Swartz 

 Genus Monoceratina Roth 



MONOCERATINA CELSALOBATA Cooper, 



n. sp. 

 Plate 1, figures 23-26 



Carapace elongate in lateral view, very 

 thick; ends rounded with a slight forward 

 swing; cardinal angles obtuse; dorsum and 

 venter very slightly convex, subparallel ; 

 ventral lobe terminates just above the ven- 

 tral margin and about the middle of the 

 posterior half; hinge straight; greatest 

 height and thickness just back of midlength ; 

 pit indistinguishable. 



Length, 0.83 mm; height, 0.30 mm; 

 thickness, 0.37 mm. 



Golconda formation, locality 17, rare. 



M. cehalobata is distinguished from M. 

 furcula Croneis and Gale by the greater 

 proportional length (form ratio) and by 

 the relatively high position of the lobes. 



Monoceratina opima Cooper, n. sp. 



Plate 1, figures 29-32 

 Carapace short and thick, valves equal, 



elongate in lateral view, ovate to acumin- 

 ate In ventral view; cardinal angles fairly 

 prominent, anterior more obtuse, posterior 

 of about 90 degrees, giving a slight forward 

 swing; dorsum slightly convex, venter 

 broadly so ; hinge straight and slightly chan- 

 nelled ; lobes terminate at and conform to 

 ventral margin; greatest height and thick- 

 ness back of midlength. 



Length, 0.59 mm; height, 0.30 mm; 

 thickness, 0.37 mm. 



Renault formation, locality 9, rare. 



This species Is distinguished by Its short, 

 thick carapace and by the conformation of 

 the spine-like lobe and the ventral margin. 



Genus Triceratina Upson 



Triceratina Upson, 1933, Nebraska Geol. Survey, 

 Bull. 8, p. 29. 



Monoceratina (part) Kellett, 1935, Jour. Paleon- 

 tology, vol. 9, p. 157. 



Pterocodella (part) Croneis and Gutke, 1939, 

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

 p. 40. 



The presence of a trinodal ostracode In 

 the basal Chester, described by Croneis and 

 Gutke as Pterocodella inconsueta, throws 

 an Interesting light upon Upson's genus 

 Triceratina. The Chester species possesses 

 a large, prominent posterior node In addition 

 to the splne-termlnated ventral node, and 

 a somewhat less prominent but wider dorsal 

 node or swelling, the latter situated above 

 the ventral node. The Chester specimens 

 show these nodes to be quite constant, 

 especially the ventral and dorsal ones, and 

 therefore the question of the synonymy of 

 these forms should be reopened. Bassler and 

 Kellett (1934, p. 12) say that "Good 

 generic characters are found In the loba- 

 tlon of the valve. . . . and variations In their 

 development always afford good specific 

 characters, and often distinguish genera" — 

 the latter referring to lobes of the Bey- 

 rich I ace a. 



M. lewisi Harris and Lallcker agrees 

 with the Renault species In all major fea- 

 tures, differing only In minor structural de- 

 tails. While the shape, size, number, and 

 position of nodes vary considerably between 

 young moults and adult specimens, the pre- 

 sence of such prominent nodes on these 

 species is significant. The occurrence, in the 

 lowest Chester, of a species so similar 

 to one from the highest Pennsylvanlan and 

 Permian beds, is Important In that it 



