24 



ILLINOIS STATE GEOLOGICAL SURVEY 



are shown by slight differences in the height 

 and thickness of the posterior bar. 



The variations in shape and length of 

 the aboral projection of the fang, as well as 

 the convexity of the anterior margin of the 

 fang, are reflected in the young. About two 

 dozen young specimens were sufficiently 

 distinctive that their relationship to the 

 adult was not recognized in an earlier study 

 (Rexroad, 1957). They were named as a 

 new species, N. striatus. The additional 

 specimens recovered from the Glen Dean 

 Formation show the variations among the 

 young and the gradation from the young 

 to the mature stage, as well as adult speci- 

 mens which still retain to some degree the 

 aberrant youthful characteristics upon 

 w^hich A^. striatus was based. Therefore^ A^. 

 striatus is placed in synonomy with A^. scitu- 

 lus. 



Material studied. — 548 specimens from 

 this study, 100 from the Rexroad 1957 

 study. 



Distribution. — Renault, Paint Creek, 

 Golconda, Glen Dean, Menard, Clore, and 

 Kinkaid Formations of Illinois, Indiana, 

 and Kentucky, and the Delaware Creek 

 Member of the Caney Shale of Oklahoma. 



Repository. — Illinois State Geological 

 Survey, 3P63, 3P64, 3P65, 3P66, 3P67 (fig- 

 ured specimens). 



Neoprioniodus varians (Branson and 



Mehl) 



Plate 5, figures 3 and 4 



Prioniodus varians Branson and Mehl, 1940, Deni- 

 son Univ. Bull., Jour. Sci. Labs., v. XXXV, p. 

 174, pi. V, figs. 7, 8; ? Bischoff, 1957, p. 49, 

 pi. 5, fig. .35; Flugel and Ziegler, 1957, p. 50, 



Neoprioniodus varians (Branson and Mehl), Rex- 

 road, Illinois Geol. Survey Rept. Inv. 199, p. 

 35, pi. 2, fig. 10. 



The Chester specimens, although varia- 

 ble, conform well to the Caney Shale forms. 

 The species is similar to N. loxus but differs 

 chiefly in the angle between the fang and 

 posterior bar from lateral view. In N. 

 varians it is about 100°, in N. loxus about 

 135°. Also, the inner lip on the aboral pro- 

 jection of N. loxus flares more markedly. 



Material studied. — 121 specimens from 

 this study, 10 from the Rexroad 1957 study. 



Distribution. — Paint Creek, Glen Dean, 

 and Clore Formations of Illinois, Indiana, 

 and Kentucky, also the Caney Shale of 

 Oklahoma. 



Repository. — Illinois State Geological 

 Survey, 3P68, 3P69 (figured specimens). 



Genus Ozarkodina Branson and Mehl, 1933 

 Type species: Ozarkodina typica Branson and Mehl 



Ozarkodina compressa Rexroad 



Plate 6, figures 1 and 2 



Ozarkodina compressa Rexroad, 1957, Illinois Geol. 

 Survey Rept. Inv. 199, p. 36, pi. 2, figs. 1, 2. 



The majority of specimens of O. com- 

 pressa found in the Glen Dean Formation 

 correspond closely to the holotype and par- 

 atype of the species. A few specimens vary 

 in being markedly more elongate than the 

 average, and some specimens are slightly 

 less arched than the remainder. Young 

 specimens have fewer denticles, a propor- 

 tionately larger subapical pit, and lack 

 germ denticles. 



Material studied. — 243 specimens from 

 this study, 25 from the Rexroad 1957 study. 



Distribution. — Golconda, Glen Dean, 

 Menard, and Kinkaid Formations of Illi- 

 nois, Indiana, and Kentucky. 



Repository. — Illinois State Geological 

 Survey, 3P70, 3P71 (figured specimens). 



Ozarkodina curvata Rexroad, n.sp. 

 Plate 4, figures 1-3 



Strongly arched and bowed, thin, blade- 

 like unit with posterior limb less arched; 

 the anterior limb typically has four or five 

 laterally compressed denticles fused about 

 two-thirds the distance to the apices; den- 

 ticles decrease slightly in size anteriorly; 

 denticles of the posterior limb number 

 about nine to eleven and are laterally com- 

 pressed, fused about one-half to two-thirds 

 distance to the apices, and of somewhat 

 varying sizes. Typically the denticles of the 

 posterior limb are smaller than denticles of 

 the anterior limb and suppressed germ den- 

 ticles are commonly present. The apical 

 denticle is twice the width of adjacent an- 

 terior denticles, is longer, tapers to a 

 point, and is laterally compressed with 



