FOSSILS FROM TIERRA DEL FUEGO AND PERU. 79] 
internal tube; 6, same with the fusiform helicoid cavity below (the ossicle is here 
inverted) ; c, outline of lower part of ossicle. 
The tube appears to enclose a rolled membrane or dissepiment, which connects and 
corresponds in its turns with the spire below. The spiral character of the fusiform 
chamber is well retained in the material which now fills it, which has this structure, and 
peels off very regularly in a spiral coat, as seen in the figure. The ossicle tapers below, 
and is obtuse at its extremity. It is about half an inch in diameter ; and the fusiform 
chamber about one half. The tube is } this diameter. On one side of the cylinder there 
is a shallow longitudinal groove. The calcareous substance of the fossil has the usual 
radiately fibrous structure of the Belemnite. 
2. Fossils from San Lorenzo, Peru. 
Triconia LorentTy (Dana).—Transversely subtriangular, lower margin arcuate. 
Sides compressed ; flank flattened, carinate, nearly smooth. Anterior to carinate surface 
marked with two series of parallel ridges meeting at an acute angle (68°, nearly) ; ridges 
of posterior series short, broader than the others, and about one-third as numerous; ridges 
of anterior series elongate, regular, all obtuse, naked, about 25 in number.—Length 23 
inches ; height 574% L. ; flank nearly 2 inch wide ; apical angle about 120°.—Plate 15, fig. 
2, shell, natural size ; 2 a, vertical section ; 4, c, hinge, imperfectly preserved. 
TuRBo . Plate 15, fig. 3.a,6,. Natural size. The length of this imperfect 
specimen is 2g inches ; aperture nearly semicircular, and 1g inches across; last whorl 
rotund, carinate below, with very low tubercles, or none, 
NavTILUs TENUI-PLANATUS (Dana).—Very large. Shell thin and broad discoid. 
Exterior without (7) markings. Septa straight, rather crowded; 12 to 2 lines apart. 
Siphuncle a short distance inside of centre-—Breadth 7 inches.—Plate 15, fig. 4. 
3. Fossil Ammonite from the Andes. 
Ammonites Prcxerrner (Dana).—Large, thick discoid, whorls ventricose ; sides cos- 
tate ; coste large, rounded, naked, simple, equal and separated by equal rounded inter- 
vals.—5 inches or more in diameter ; last whorl at least 17 inches through, in the direc- 
tion of the diameter of the shell; the next on the same diameter hardly half this breadth. 
Coste of outer whorl a fourth of an inch broad.—Plate 15, fig. 5, exterior cast, natural 
size. 
This specimen was obtained by my friend and associate in the Expedition, Dr. C. 
Pickering, at an elevation of 16,000 feet, on the route to Sierra de Pasco. As we have a 
cast of only one side, the character of the back of the whorls is not ascertained. 
Notr.—Plate 15, figure 6, represents an Ammonite from a rolled fragment obtained 
at Truxillo, examined in a collection of fossils at Lima, and drawn by permission. It is 
near the A. communis, but the whorls in 4 cross section (6a) are more nearly rotund, 
and have a slight depression along the back. The coste are equal, acute, naked, bifid 
along the back, and separated by concave sulci. Diameter 23 inches. Last whorl about 
8 inch across, costee about 13 lines apart. 
181 
