44 SPECIES OF EXOGYEA PROM THE EASTERN GULP REGION AND THE CAROLINAS. 



In North Carolina the species is restricted to the marine invertebrate-bearing beds forming 

 the upper part of the Black Creek formation. It has been collected from four localities dis- 

 tributed along a linear distance of approximately 35 miles. The varietal form of the species, 

 Exogyra ponderosa var. erraticostata var. nov., has approximately the same range and distribu- 

 tion as the typical form. This variety has been collected from 24 authentic localities in the 

 eastern Gulf region and from two localities in the Black Creek formation of the Carolinas. 

 Specimens questionably referred to this variety have been found at two localities in North 

 Carolina in beds near the base of the overlying Peedee sand, indicating a slightly higher 

 range than the known range of the variety in the eastern Gulf region. 



Exogyra costata Say ranges from just above the upper limit of the range of Exogyra pon- 

 derosa Roeiner, through the upper half of the Sehna chalk and its nonchalky equivalents which 

 include all of the Ripley formation of northern Mississippi, and the upper one-half or two- thirds of 

 the Ripley formation of eastern Alabama and Georgia. Apparent exceptions to this limit of 

 range are a few specimens found in the Exogyra ponderosa zone, which appear to approach 

 rather closely to the typical costate forms, but all of which are smaller and differ slightly in 

 form, shape, and arrangement of costse from well-developed typical specimens. These are 

 probably the ancestors of the true Exogyra costata of higher horizons. Geographically this 

 species occurs in a belt south and west of that occupied by Exogyra ponderosa, extending from 

 Macon County, Ga., westward through Alabama and northward through Mississippi to the 

 Tennessee State line, a distance of 400 miles. The collections studied include specimens from 

 81 localities, but this number could be greatly increased were the region covered in detail. 



In the Carolinas the species ranges through the Peedee sand. It has been obtained from 

 2S localities, distributed hi a belt extending from Peedee River in South Carolina northeastward 

 to the southern part of Pitt County, X. ('., a distance of approximately 150 miles. 



Exogyra costata var. cancellata var. nov. makes its first appearance approximately coin- 

 cident with the initial appearance of the typical, strongly costate forms, the horizon of both 

 being just above the upper limit of the range of Exogyra ponderosa Roemer. In the lower- 

 most beds of its stratigraphic range, especially in Mississippi, this variety appears to exceed 

 numerically the typical costate forms. In the successively higher beds it appears to decrease 

 in numbers and is entirely absent, so far as known, from the upper 50 or 75 feet of Cretaceous 

 strata in Mississippi and western Alabama and probably from a greater thickness in the Chat- 

 tahoochee region. 



This varietal form has been collected from 27 localities in the eastern Gulf region. Of 

 these localities 26 are distributed through a belt lying south and west of that in which Exogyra 

 ponderosa Roomer occurs and extending from Johnsons Hill, 4 miles north of Lumpkin, in 

 Stewart County, Ga., westward through Alabama and northward through Mississippi to 7 miles 

 east of Lexington, Henderson County, Term., a distance of approximately 400 miles. The 

 twenty-seventh locality is near Cairo, 111., where one specimen was found in an excavation 

 for one of the piers of the Illinois Central Railroad bridge over Ohio River. (See p. 18.) 



In North Carolina the variety has been obtained from four localities only, the horizon hi 

 each place being toward the basal part of the Peedee sand. 



NEW JERSEY. 



Both Exogyra ponderosa Roemer and Exogyra costata Say have been recognized in the 

 Upper Cretaceous deposits of New Jersey. According to Weller 1 they are here restricted in 

 range in the same manner as their southern representatives. Exogyra ponderosa occurs only 

 in the Marshalltown clay marl, which is next to the highest of the formations of the Matawan 

 group; and Exogyra costata occurs throughout the Monmouth group, which overlies the Mata- 

 wan group. So far as known the two species do not overlap in the New Jersey section and 

 hence they afford a valuable means of correlation. 



i Welter, Stuart, The Cretaceous paleontology of New Jersey: New Jersey Geol. Survey, Paleontology, vol. 4, text, 1907, pp. 456-J60. 



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