176 APPENDIX E. PALAEONTOLOGY. 



Productus coea, D'Orbig. 



Prod, cora, D'Orbig., 1842, Palaeont. Voy. dans l'Amer. Merid., p. 55, 

 pi. 5, fig. 8, 9, 10. 



P. tenuistriatus, Verneuil, 1845, Geol. Russ. et. Ural., vol. 2, p. 260, 

 pi. 16, fig. 6. 



P. cora, Koninck, 1847, Monog. du Genre Prod, et Chonetes, p. 50, 

 pi. iv. a, b, et pi. v, fig. 2, a — d. 



The specimens from Arkansas are all imperfect, yet tbey are plainly 

 referable to this species. It is one of the most characteristic fossils of 

 the carboniferous beds of Kentucky, Indiana, Illinois, and Missouri. It 

 occurs in Washington and Crawford counties, in gray sub-crystalline 

 limestone. 



Productus costatus, Sowerby.* 



Paleontology, PI. 1, fig. 2. 



This Productus occurs with the preceding species, in Washington 

 county, Arkansas, and, like it, has a very extended geographical range 

 in this country and Europe. 



» 



Terebratula subtilita, Hall. 



PALEONTOLOGY, PI. 4, fig. 8. 



Terebratula subtilita, Hall, Stansbury's Expedition to Great Salt Lake, 

 409, pi. xi, fig. 1, a — b, 2, a — c. 



This shell is very common in the superior members of the carbonife- 

 rous formation in Illinois, Indiana, and Kentucky, where it usually is 

 found with Archimedipora archimedes, Pentremites florealis, and Pro- 

 ductus punctatus. Its vertical range being rather limited, it constitutes 

 one of our most useful guides in studying the relative position of the 

 various members of the carboniferous strata. This shell is very variable 

 in its characters, so that we are liable to multiply species from its varie- 

 ties, unless a number of specimens are under examination. Some indi- 

 viduals are very much inflated ; the dorsal valve exhibits a profound 



* For synonyms and references see Koninck' s Monog. du Gen. Prod, et Cho- 

 netes, p. 92. 



