﻿324 CONRAD'S DESCRIPTIONS OF 



This beautiful series of cretaceous forms seems to be very limited in geographical 

 distribution, so far as our present knowledge extends. It is probably unknown as 

 yet beyond the limits of Tippah County, which borders on Tennessee. No account 

 has been given of such a group by the State Geologists of Tennessee or Alabama. 

 Dr. Spillman informs me, " The fossils you have now under examination were found 

 in the bluffs of Owl creek, three miles north of the town of Ripley," and he concurs 

 in opinion with me that they might properly be named the " Ripley group." He also 

 remarks that Ammonites placenta occurs in it with the shell preserved, and that in 

 connection with the Ripley group, or in the same locality, are " Exogyra costata, 

 * Gryphcea mutabilis, Ostrea plumosa, Natica petrosa, Nautilus Dekayi, &c, with the 

 shell more or less preserved, in]an argillo-calcareous marl," but none of these species are 

 contained in his collection sent me from Tippah County. 



Professor Harper, in his report for 1857, describes some of the localities of the above 

 group near Ripley, and names many of the genera of its contained fossils. 



It would perhaps be convenient to designate these strata Upper Cretaceous, in 

 contradistinction to the limestones and marls beneath, which are palaeontologically so 

 distinct. 



AGEPHALA. 

 PHOLADOMYA, Sowerby. 



Pholadomya tippana. PI. 34, fig. 9. Acutely subovate, very thin, profoundly 

 ventricose, with numerous radii, curved and dichotomous on the anal side. 



An imperfect specimen, with a portion of the shell, has been restored to an ap- 

 proximate outline in the figure. The sculpture is in sufficient preservation to charac- 

 terise the species. 



PERIPLOMA, Schum, 



Pepjploma applicata. Oblong-oval, equilateral, compressed, thin and fragile ; 

 right valve convex-depressed ; left valve flattened or slightly concave, with an oblique 

 anterior carinated line ; valves smooth in the middle, roughened with rugose concen- 

 tric lines posteriorly ; anterior end truncated or obtusely rounded, nearly direct ; basal 

 margin contracted in the middle. 



Length II inches. 



■&* 



SILIQUARIA, Helium. 



Siliquapja biplicata. PI. 34, fig. 17. Thin, convex, with two radiating folds or 

 depressions anteriorly ; basal line slightly contracted or incurved ; anterior side short. 



'Ostrea vcsicularis. Lam- 



