M 
GEOLOGY 
Locality. — The Ammonites Shumardi appears to be quite rare; I have only seen the specimen 
lipured vrhich was found in the Cretaceous rocks on the borders of Red river near Preston, Texas. 
1 have dedicated it to the learned geologist of Arkansas , my friend Dr. George G. Shiunard of 
Fort Smith. 
Explanation of figures. — Plate 1, fig. 1. Shell natural size, side view. The second row of tubercles , near the 
back , is only visible on a part of the last whorl ; the specimen being 
very much worn. 
Plate I, fig. 1 a. The same, back view. This part of the keel has been destroyed, and 
instead of being sharp it is hollowed into the back ; but it is prominent 
on the whorl that is covered by the mouth. 
AMMONITES BELKNAPII n. sp. 
Plate II , fig. la, lb. 
Description. — Shell oval, compressed, subdiscoidal, sharp and strongly carinated. The sides are ornamented 
with large rounded ribs , widening towards the back , slightly flexuous ; they usually occupy the entire breadth of 
the sides but some irregularly distributed stop at two thirds the distance , beginning at the back. Although this 
specimen has lost its central portion , it is easy to see that the spire increases very rapidly and that the whorls are 
compressed and two thirds concealed by each other. The last whorl is almost as large as half the diameter of the 
entire shell. In regard to the keel, the ribs do not correspond, but alternate, as fig. 1 b shows very distinctly. 
Septa with four Irifid lateral lobes widely separated and very distinct upon this specimen 
Observations. — This species resembles very much the Ammonites cultratus d’Orb. [PaUontologie Frangaise, 
Terrains Critacis, tome I, page 144, plate 46.) found in the upper Neocomian at Escragnole, in the de- 
partment of the Var, and I am by no means sure they are not identical. In the Am. cultratus the ribs 
appear more flexuous, more numerous, and the whorls are less hidden by each other, that is the spire 
is larger. As to the Ammonites flaccidicosta Roem. [Die Kreidebildungen von Texas , page 33 , plate I , fig. 
1 a, 1 b.) it differs in having no keel, cylindrical whorls, a sort of tubercle alternating on the ribs near 
the umbilicus ; and by the convergence of the ribs which meet at the back or are only separated b\ 
a line. 
Locality. — The only specimen I possess and the only one 1 have seen , was found in the Cre- 
taceous rocks near the town of Preston, Texas, in the bed of a little creek flowing into Red river. 
I have dedicated this species to A. E. Belknap, Esq. of Boston, so well known for his beautiful 
collection of living shells. 
Explanation of figures. — Plate II, fig. 1 a. Side view. 
» II , fig. 1 b. Back view' of a portion of the same specimen , showing the keel 
and especially the alternation of the ribs. 
AMMONITES PERGVIANUS de Buch. 
Plate V, fig. 1 , 1 a , 1 b. 
Description. — Shell much compressed, discoidal, sharply carinated, ornamented with ribs, simple, distinctly 
elevated and much larger than the intervals that separate them ; the ribs are slightly flexuous , narrow at the um- 
bilicus and widening to within a short distance of the dorsal edge , where they are again more contracted ; they all 
begin at the umbilicus on the small specimen fig. 1 a , with the exception of two that begin at a third of the distance 
from the umbilicus. Dorsal carina prominent , sharp , smooth , marked on each side by a shallow depression ; the 
ribs do not cross the dorsal carina , but stop on each side at the shallow depression. The lobes are very large ; 
the upper lateral lobe is placed at the middle of the side , and the lower lateral lobe almost touches the edge. The 
last spire near the mouth envelops very imperfectly the preceding one. 
Observations. — Alex, von Humboldt in ascending the Rio Maranon (Upper Amazon) from Tomependa 
to Caxamarca, at the little village of Montan, Peru, on the dividing ridge of the Cordilleras, 2800 metre.s 
