GLEN DEAN CONODONTS 



25 



sharp edges fore and aft, inclined slightly 

 posteriorly. The navel is very small, mod- 

 erately deep, asymmetric in outline, with 

 the inner margin nearly straight, the outer 

 margin with slightly flaring lip, the pos- 

 terior end pointed and continued as a faint 

 groove along the aboral margin of the pos- 

 terior bar. The anterior end of the navel 

 is rounded. 



Chief variation in this species is in the 

 size of the denticle on the posterior limb. 

 Limbs of some specimens bear denticles of 

 a single size, but on other specimens den- 

 ticles are of varying sizes. 



Because the posterior limb is longer than 

 the anterior limb, is bowed but otherwise 

 nearly straight, and because the denticles 

 on it may vary in size, this species bears a 

 resemblance to the group of hindeodellids 

 in which the anterior process is sharply 

 downturned in a "pick-like" manner. 



Material studied. — 38 specimens. 



Distribution. — Renault and Glen Dean 

 Formations of Illinois, Indiana, and Ken- 

 tucky. 



Repository. — lUinois State Geological 

 Survey, 3P72 (holotype), 3P73, 3P74 (para- 

 types). 



Genus Spathognathodus Branson and 

 Mehl, 1941 



(Spathodus Branson and Mehl, 1933) 



Type species: Spathodus primus Branson and Mehl 



Spathognathodus campbelli Rexroad 



Plate 6, figure 9 



Spathognathodus campbelli Rexroad, 1957, Illinois 

 Geol. Survey Rept. Inv. 199, p. 37, pi. 3, figs. 

 13-15. 



The representatives of this species found 

 in the Glen Dean closely resemble the pre- 

 viously described specimens. 



Material studied. — 12 specimens from 

 this study, 65 from the Rexroad 1957 study. 



Distribution. — Renault, Paint Creek, 

 Golconda, Glen Dean, Menard, and Kin- 

 kaid Formations of Illinois, Indiana, and 

 Kentucky. 



Repository. — Illinois State Geological 

 Survey, 3P79 (figured specimen). 



Spathognathodus cristula Youngquist 



and Miller 



Plate 6, figures 3 and 4 



Spathognathodus cristula Youngquist and Miller, 

 1949, Jour. Paleontology, v. 23, no. 6, p. 621, 

 pi. 101, figs. 1-3; Rexroad, 1957, Illinois Geol. 

 Survey Rept. Inv. 199, p. 38, pi. 3, figs. 16, 17. 



This is one of the least variable and most 

 abundant Glen Dean species. All speci- 

 mens are very similar to the holotype and 

 para types. 



Material studied. — 367 specimens from 

 this study, 50 from the Rexroad 1957 study. 



Distribution. — Renault, Paint Creek, 

 Golconda, Glen Dean, Menard and Clore 

 Formations of Illinois, Indiana, and Ken- 

 tucky, and the Pella Beds of Iowa. 



Repository. — Illinois State Geological 

 Survey, 3P80, 3P81 (figured specimens). 



Spathognathodus spiculus Youngquist 



and Miller 



Plate 6, figures 5-7 



Spathognathodus spiculus Youngquist and Miller, 

 1949, Jour. Paleontology, v. 23, no. 6, p. 622, 

 pi. 101, fig. 4; Rexroad, 1957, Illinois Geol. 

 Survey Rept. Inv. 199, p. 38, pi. 3, figs. 18-21. 



Spathognathodus bidens Youngquist and Miller, 

 Jour. Paleontology, v. 23, no. 6, p. 621, pi. 101, 

 fig. 5. 



The Chester representatives of this spe- 

 cies show a great amount of variation, par- 

 ticularly in the number and shape of the 

 major anterior denticles. The large num- 

 ber of specimens available show a unity in 

 this variable group and include specimens 

 nearly identical to the holotype of S. bidens 

 as well as of S. spiculus indicating that the 

 two represent a single species. Because the 

 great majority of specimens conform more 

 closely to S. spiculus, that name is retained 

 in preference to S. bidens. 



Material studied. — 175 specimens from 

 this study, 90 from the Rexroad 1957 study. 



Distribution. — Renault, Paint Creek, 

 Golconda, Glen Dean, Menard, Clore, and 

 Kinkaid Formations of Illinois, Indiana, 

 and Kentucky, and the Pella Beds of Iowa. 



Repository. — Illinois State Geological 

 Survey, 3P82, 3P83, 3P84 (figured speci- 

 mens). 



