34 



CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



The evidence afforded by the fossil plants is in harmony, therefore, with that afforded by 

 the fossil invertebrates so far as the correlation of the formation with the Black Creek formation 

 of the Carolinas is concerned. As regards the New Jersey Cretaceous, however, Berry appa- 

 rently regards the beds as corresponding to a somewhat earlier horizon than that indicated by 

 the invertebrates — namely, to the Magothy formation. However, he admits elsewhere 1 that 

 the Magothy flora possibly persisted to a later time in the Carolinas and Georgia than in New 

 Jersey. 



EXOGYRA COSTATA ZONE. 2 



RANGE OF THE SPECIES. 



Typical specimens of Exogyra costata Say make their first appearance just above the zone 

 of Exogyra ponderosa and range upward to the top of the Cretaceous. The lower limit of this 

 range is indicated on Plates IX and X by red line 2, and the upper limit is coincident with the 

 upper surface of the typical marine Cretaceous beds of the region. Between these two limits 

 the species has a general geographic distribution throughout the typical marine beds. 



The name Exogyra costata is therefore obviously appropriate as a zonal designation. The 

 species, including its varietal form Exogyra costata var. cancellata Stephenson, has been collected 

 from 90 authentic localities within the geographic limits of the zone in the eastern Gulf region. 

 This number could be multiplied many times by detailed collecting. 



Young individuals of the genus with well-developed, fairly typical costae, some approaching 

 the average size of the adult Exogyra costata, have been found at rare intervals below the lower 

 limit of the zone of Exogyra costata as indicated — that is, have been found in the zone of Exogyra 

 ponderosa. Such specimens may perhaps be regarded as the ancestors of the well-developed 

 costate forms of higher horizons. 



In the eastern Gulf region 185 species, questionably 187, are known in the zone of Exogyra 

 costata. These are as follows: 3 



Fossils from Exogyra costata zone. 



Echinodermala: 



Cassidulus porrectus Clark, a. 



C. subconicus Clark, a. 



C. conoideus Clark, a. 



C. micrococcus Gabb. a. 



C. subquadratus Conrad, a c. 



C. intermedius Slocum. a. 



Hemiaster ungula (Morton), a. 



II. parastatus (Morton), a. 



II. lacunosus Slocum. «. 



?Coptosoma mortoni (De Loriol 



Rhizocrinus alabamensis De Loriol. i 



?Linthia variabilis Slocum. a. 

 Vermes: 



Serpula cretacea (Conrad), a b. 



S. barbata Morton, a. 



S. sp. (nearly straight tube), a c. 



Hamulus onyx Morton, a b c. 



H. squamosus Gabb. a b c. 

 Molluscoidea: 



Terebratulina floridana (Morton), a. 



T. filosa Conrad, a. 

 Mollusca: 



Nucula percrassa Conrad, abed. 



N. cuneifrons Conrad, a. 



N. eufalensis Gabb. a. c. 



Leda pinnaforma Gabb. a b. 



Mollusca — Continued. 



Leda longiirons Conrad, a b c. 



L. protexta Gabb. a b. 



Perrisonota pro texta Conrad . a c. 



Cucullsea vulgaris Morton, a. 



('. antrosa Morton, a. 



C. littlei (Gabb). a. 



Trigonoarcasp. nov. (found at "The Caves," Miss.), a. 



Breviarca cuneata (Gabb). a. 



Nemodon eufalensis (Gabb). a. 



X. brevifrons Conrad, a b. 



Area rostellata Morton, a. 



tilycymeris subaustralis (D'Orbigny). a b. 



Pinna laqueata Conrad, a. 



Gervilliopsis ensiformis (Conrad), a b c. 



G. sp. nov. a. 



Inoceramus argenteus Conrad, a. 



Pteria petrosa (Conrad), a. 



Ostrea subspatulata Forbes, a. 



0. plumosa Morton, ab c. 



O. tecticosta Gabb. ab c. 



0. larva Lamarck, a b. 



O. peculiaris Conrad, a. 



O. panda Morton, ab c. 



O. sp. nov. (very irregular), a b. 



0. sp. nov. (long, thin, irregular), a. 



Gryphaea vesicularis Lamarck, a b. 



i Berry, E. W, The Upper Cretaceous and Eocene floras of South Carolina and Georgia: Prof. Paper IT. S. Geol. Survey No. 84 (in press). 



3 See pp. -ll-oo. 



'a, Exogyra costata zone; 6, Eiogyra ponderosa zone above Mortoniceras subzone; c, Mortoniceras subzone; d, basal beds of Eutaw formation. 



