APPENDIX E. PALAEONTOLOGY. 183 



Ammonites vespertinus, Morton. 



Ammonites vespertinus, Morton, Synopsis Cretaceous Group U. S., 

 40, pi. xvii, fig. 1. Id., D'Orbigny, Prodrome de Palseont. II, 212. 



Shell large, volutions about three ; vertical section sub-quadrangular ; 

 ribs prominent, each garnished with three nodules, dorsal one most 

 prominent ; dorsal margin furnished with a prominent rounded carina. 



This is the largest species of Ammonite that has hitherto been found 

 in the United States. In the cretaceous strata near Fort Washita, 

 specimens were found to measure nearly three feet in diameter, and 

 estimated to weigh upwards of two hundred pounds. It is quite com- 

 mon. The fragment described by Dr. Morton was obtained from the 

 plains of Kiamesha, Arkansas. 



Ammonites marciana, Shumard. 

 Paleontology, PL 4, fig. 5. 



Shell compressed, not carinated, with about twelve simple, prominent 

 rounded ribs, which cross the dorsum and sides of the last volution 

 obliquely, without interruption; dorsum convex, whorls compressed; 

 surface smooth in the intervals between the ribs ; aperture longitudinal, 

 sub-oval. 



Length of last whorl 1 1 lines, width of do. 4-| lines ; width of umbi- 

 licus 3 lines. 



The specimen figured is a cast, and the character of the lobes of the 

 chambers cannot be made out. 



Occurs in the cretaceous strata of Cross-Timbers, Texas. 



Ammonites acuto-carinatus, Shumard. 

 Paleontology, PL 1, fig. 3. 



Shell much compressed, sharply carinated, ornamented with from 30 

 to 34 transverse ribs; ribs simple, distinctly elevated, flexuous, commen- 

 cing narrow at the umbilicus, and widening to within a short distance of 

 the dorsal border, where they are again somewhat contracted ; dorsal 

 carina prominent, sharp, smooth, marked on each side by a shallow 

 depression ; aperture elongate-cordate, lateral septa trilobate. 



Diameter 2 4-10 inches ; thickness of last whorl near aperture 5->10 

 inch. 



