16 



ILLINOIS STATE GEOLOGICAL SURVEY 



LOG. 13-GERKIN QUARRY 



a. 



E 





Sandstone, gray to yellowishi- /__;__, 

 tan, and sandy shale, ^ yi^r^x^ 

 tiigtily ferruginous 12 / _^ 



h:i9 



if 



Q.> 





f\ 1 1 



B: 



zr 

 < 

 lij 



Q 

 UJ 



_) 



CD 



Limestone, gray, medium- 

 groined, fossiliferous, 

 crinoidal 18' 3" 



( 





1 1 1 rn 'S 



{ 1 B- 



1 1 1 5- 



1 1 BliO 



' ' B 



^ 1 1 Bl 5 



1 1 & 



f 



1 1 1 BS^ 1 



Fig. 13. — Gerkin Quarry, locality 13. Small aban- 

 doned quarry about 2.9 miles NW of Shoals, 

 NW14 SWi/4 sec. 12, T. 3 N., R. 4 W., Shoals 

 quadrangle, Martin County, Indiana. 



Genus Cavusgnathus Harris and Hollings- 

 worth, 1933 



Type species: Cavusgnathus alta Harris and Hol- 

 lingsworth 



Cavusgnathus convexa Rexroad 

 Plate I, figures 12-14 



Cavusgnathus convexa Rexroad,, 1957, Illinois Geol. 

 Survey Rept. Inv. 199, p. 17, pi. 1, figs. 3-6. 



The holotype and the two paratypes of 

 this species are from the Glen Dean Forma- 

 tion in the type area of the Chester Series, 

 and specimens from other Glen Dean loca- 

 tions conform closely to the type specimens. 

 The large number of specimens examined 

 in this study show clearly the changes which 

 occurred during ontogeny. Young speci- 

 mens tend to be narrow with nearly straight 

 parapets. With growth they tend to broaden 

 the platform without a proportional in- 

 crease in length, increase the flare of the 

 inner lip of the navel, and some gerontic in- 

 dividuals show additional denticles on the 



anterior margin of the blade, increasing the 

 number of blade denticles from the typical 

 four, five, or six to as many as nine. Vari- 

 ants which in oral outline show blades less 

 regularly convex than any previously known 

 are also present in the Glen Dean collec- 

 tions. 



Material studied. — 201 specimens from 

 this study, 35 from Rexroad 1957 study. 



Distribution. — Renault, Golconda, Glen 

 Dean, Menard, and Kinkaid Formations of 

 Illinois; Glen Dean of Indiana and Ken- 

 tucky. 



Repository. — Illinois State Geological 

 Survey, 3P1, 3P2, 3P3 (figured specimens). 



Cavusgnathus cristata Branson and Mehl 

 Plate 1, figures 15-17 



Cavusgnathus cristata Branson and Mehl, 1940, 

 Denison University Bull., Jour. Sci. Labs., v. 

 XXXV, p. 177, pi. V, figs. 26-31. Hass, 1953, U. 

 S. Geol. Survey Prof. Paper 243-F, p. 77, pi. 14, 

 figs. 12-14. Cooper^ (part) 1947 Jour. Paleon- 

 tology, V. 21, no. 2, p. 91, pi. 20, figs. 4-6 (not 

 figs. 7-10). Elias, 1956, Petroleum Geology of 

 southern Oklahoma: Am. Assoc. Petrol. Geol., 

 V. 1, p. 115, pi. II, figs. 1-6.? BiscHOFF, 1957, p. 

 19, pi. 2, figs. 7a, b. 



Cavusgnathus cristata var. grandis Elias, 1956, Pe- 

 troleum Geology of southern Oklahoma: Am. 

 Assoc. Petrol. Geol., v. 1, p. 115, pi. II, figs. 

 12-14. 



Some of the Glen Dean specimens con- 

 form quite closely to Branson and Mehl's 

 holotype of C. cristata, but most have a 

 more regular outline of the oral margin of 

 the blade as viewed laterally, thus resem- 

 bling C. convexa. There are a number of 

 differences, however, between C. convexa 

 and C. cristata. The navel of C. convexa 

 extends to the posterior tip of the specimen 

 and is very asymmetric with greater flare of 

 the inner lip in contrast to the greater sym- 

 metry of the navel of C. cristata which ex- 



explanation of plate 5 



All figures X 40 



Numbers in parentheses after explanations refer to locality and sample numbers, for example 



(12-3) refers to locality 12, sample 3. 



Figure 



1, 2 Genus indeterminate; posterior views (12-3 and 1-40). 



3, 4 Neoprioniodus varians (Branson and Mehl); inner lateral views (11-20 and 8-4). 



5, 6 Neoprioniodus camurus Rexroad; inner lateral views (12-2 and 12-4). 



7-9 Neoprioniodus loxus Rexroad; 7, 8, inner lateral views (1-12 and 13-2); 9, outer lat- 



eral view (2-22). 



10-14 Neoprioniodus scitulus (Branson and Mehl); 10, 11, inner lateral views of young 



specimens (12-29 and 1-38); 12-14, inner lateral views of mature specimens (1-41, 10-4, 

 and 1-41 respectively). 



