GLEN DEAN CONODONTS 



21 



Repository. — Illinois State Geological 

 Survey, 3P31 (holotype), 3P32, 3P33, 3P34, 

 3P35, 3P36 (paratypes). 



Genus Ligonodina Bassler, 1925 



Type species: Ligonodina pectinata Bassler 



Ligonodina hamata Rexroad 

 Plate 3, figures 9-14 



Ligonodina hamata Rexroad, 1957, Illinois Geol. 



Survey Rept. Inv. 199, p. 32, pi. 1, figs. 24, 25. 

 Ligonodina sp., ibid., p. 33, pi. 1, figs. 20, 21. 

 Ligonodina sp., Youngquist and Miller, 1949, Jour. 



Paleontology, v. 33, no. 6, pi. 101, fig. 11 (not 



figs. 12, 13). 



Specimens of Ligonodina from the Glen 

 Dean Formation show that the specimens 

 designated by Rexroad (1957) as Ligono- 

 dina sp., although not typical of L. hamata, 

 must be regarded as belonging to this spe- 

 cies. It seems likely that L. hamata devel- 

 oped from L. obunca by the shift of the 

 inner lateral process to the anterior margin 

 of the terminal fang. This was followed by 

 further development of the proximal por- 

 tion of the inner lateral process. The speci- 

 mens previously referred to as L. sp. by 

 Rexroad represent the extreme develop- 

 ment of this trend but as a variation from 

 the norm. The additional material also 

 shows that four discrete denticles are com- 

 monly present on the inner lateral process. 

 After further study of specimens from both 

 the Pella Beds and the Glen Dean Forma- 

 tion, the figured specimen designated above 

 and referred to L. sp. by Youngquist and 

 Miller (1949) is referred to L. hamata. 



Material studied. — 1 1 1 specimens from 

 this study, 45 from 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, 3P37, 3P38, 3P39, 3P40, 3P41, 3P42, 

 (figured specimens). 



Ligonodina obunca Rexroad 



Plate 3, figures 7 and 8 



Ligonodina obunca Rexroad, 1957, Illinois Geol. 

 Survey Rept. Inv. 199, p. 32, pi. 1, figs. 22, 23. 

 Ligonodina sp., Youngquist and Miller, 1949, 



Jour. Paleontolos^y, v. 23, no. 6, p. 620, pi. 101, 

 figs. 12, 13 (not fig. 11). 



Study of many complete specimens shows 

 that the inner lateral process of L. obunca 

 typically bears four discrete denticles and 

 that the presence of three or five denticles 

 is less common. The original description of 

 the species stated that the process bore 

 three (or rarely four) denticles. It is partly 

 for this reason that Ligonodina sp. of 

 Youngquist and Miller as represented by 

 two of their figured specimens is now placed 

 with L. obunca. In young specimens of L. 

 obunca the posterior bar is much thinner 

 and the denticles on it more prominent 

 than on adult specimens. Greatest thicken- 

 ing occurs along the anterior portion of the 

 bar. 



Material studied. — 423 specimens from 

 this study, 65 from Rexroad 1957 study. 



Distribution. — Renault, Paint Creek, 

 and Glen Dean Formation of Illinois, In- 

 diana, and Kentucky, and the Pella Beds of 

 Iowa. 



Repository. — Illinois State Geological 

 Survey, 3P43, 3P44 (figured specimens). 



Ligonodina roundyi Hass 



Plate 3, figures 1-4 



Ligonodina roundyi Hass, 1953, U. S. Geol. Survey 

 Prof. Paper 243-F, p. 82, pi. 15, figs. 5-9; Elias, 

 1956, Petroleum Geology of southern Okla- 

 homa: Am. Assoc. Petrol. Geol., v. 1, p. 126, pi. 

 V, figs. 10-14. 



The Glen Dean specimens conform very 

 closely to Hass's type specimens. The den- 

 ticles of the inner lateral process of some 

 Glen Dean specimens are not noticeably 

 compressed. The amount and symmetry of 

 the expansion of the base of the main cusp 

 is variable, as is also true of Hass's type 

 specimens. 



Material studied. — 32 specimens. 



Distribution. — Glen Dean Formation of 

 Illinois, Indiana, and Kentucky, Barnett 

 Formation of Texas. 



Repository. — Illinois State Geological 

 Survey, 3P45, 3P46, 3P47, 3P48 (figured 

 specimens). 



