GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 Moderately large, slender. Whorls strongly inflated, sculptured with strong subequal spirals, 5 on intermediate whorls, 5 or 6 on late whorls. Late whorls bearing a gradually enlarging secondary spiral between anteriormost primary and suture, and between posteriormost and suture. Well-preserved whorls showing microscopic spirals between primaries. Sculpture of early whorls and growth line not known.
 Height (incomplete, 3+ whorls) 39 mm, diameter 21 mm (figured specimen).
 Type: Paleontological Research Institution, Ithaca, N. Y., 2051.
 Type locality: Caleto Mero, Peru, Heath formation (late Oligocene).
 Turritella meroensis occurs in the middle member of the Caimito formation in the Gatun Lake area and in the Quebrancha limestone member of the same formation in the Quebrancha syncline. Preservation of the specimens from the Quebrancha limestone member is poor. This species has already been recorded by Olsson (1942, p. 239) from strata in the Canal Zone now assigned to the Caimito formation, and he thought also that Joukowsky's T. gatunensis is T. tristis or T. meroensis (Olsson, 1942, p. 241). Wherever T. meroensis has been found, in Perd, Ecuador, and PanamA, it occurs in formations of late Oligocene age.
 The later whorls of this Turritella are Mesalia-like, as pointed out by Olsson. The specimens from the Caimito formation closely agree with the form from the type locality shown in Olsson's figure 1 and with Joukowsky's illustrations of his T. gatunensis from late Oligocene strata in the Santiago area, Panama, and also with specimens from that region. The growth line is not shown on specimens from the Caimito formation. On specimens from the type locality the sinus is of moderate depth and its apex is near the middle of the whorl; the growth-line angle is narrow. Also on specimens from the type locality the growth lines form threads on unworn primary spirals.
 T. vientoensis Clark (in Clark and Durham, 1946, p. 27, pl. 23, figs. 2, 11-13, 17, 18), a late Eocene species from Colombia, is closely allied to T. meroensis, but the later whorls of T. vientoensis have more numerous spirals. T. saltoensis Clark (in Clark and Duiham, 1946, p. 26, pl. 23, fig. 28) evidently is a form of T. vientoensis differing in details of sculpture.
 There are no known descendents of T. meroensis. Though this well-defined species was identified by Joukowsky as T. gatunensis, it needs no comparison with that species. According to the growth line and the early sculpture of two spirals (Olsson, 1931, p. 76), T. meroensis is a representative of Merriam's T. uvasana stock, which is not known to have survived the Oligocene. The heavy spirals and strongly inflated whorls


suggest affinity with T. variata lorenzana Wagner and Schilling (Merriam, 1941, p. 99, pl. 18, fig. 3, pl. 19 figs. 9, 12-14), of the Oligocene of California.
 Gabb's illustrations of his T. gatunensis (Gabb, 1881, p. 342, pl. 44, fig. 10, 10a), which does not even remotely resemble T. gatunensis and was named T. tristis by Brown and Pilsbry (1911, p. 358, footnote), suggest ,, species resembling T. meroensis, but more slender. Three incomplete specimens are in the type (and only) lot (Acad. Nat. Sci. Philadelphia 3532). The largest, which has a height of 28 millimeters and a diameter ot 8 millimeters, evidently is the original of Gabb's freely drawn figure 10 and is herewith designated the lectotype. The whorls enlarge very slowly. The earliest whorls are bicarinate, but also have a weak posterior spiral; at the same stage T. meroensis has similar sculpture. A fragment of late whorls has five primary spirals, the third from the base being carinate. The: third specimen, also a fragment of late whorls, is sculp.. tured with five primary spirals and very fine secondaries; that is, the sculpture is much like that of late: whorls of T. meroensis. On the basis of this inadequate. material T. tristis may be a very slender ally of T. meroensis. The stratigraphic relations of the black shale: on Oronli Creek, in southern Costa Rica-the type. locality of T. tristis-are unknown, but, according to the fossils Gabb found there, its age probably is Oligocene. Apparently no geologist has seen it since Gabb's visit.
 Occurrence: Middle member of Caimito formation (late Oligocene), Gatun Lake area, locality 56. Quebrancha limestone member of Caimito formation (late Oligocene), Quebrancha syncline, locality 62. Late' Oligocene, Santiago area, Panama. Late Oligocene, Posorja, Ecuador. Heath formation (late Oligocene), Perd.
 Subgenus?
 Turritella cf. T. caleta Olsson
 Plate 15, figures 14-16
 Small, slender, more or less bicarinate. Early whorls sculptured with three equally spaced spirals. Anterior and posterior spirals emphasized on intermediate whorls, producing a bicarinate outline, and generally emphasized on late whorls. Intermediate and late whorls also' sculptured with unequal minor spirals, including original middle spiral. Primary and some minor spirals of well-preserved specimens slightly noded by growth lines. Growth-line sinus deep, apex slightly back of middle of whorl; growth-line angle very narrow.
 Height (incomplete, 2+ whorls) 13.5 mmn, diameter 9.5 mm (figured fragment of large specimen). Height (incomplete, 4 whorls) 13 mm, diameter 6.5 mm (figured fragment of specimen of intermediate size).


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