GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


ing, which completely exposes the anterior spiral and the part of the whorl lying immediately in front of it (pl. 16, fig. 6). This is not a late-growth feature, for some specimens of intermediate size have carinate whorls and many large specimens have tightly clasped whorls. On the typical flat-whorled form the suture is obscured by the overhanging anterior spiral. However obscure the suture may be, the base of a whorl may be identified by the narrow space between the anterior and middle spirals. Apparent variation affecting minor sculptural features may be due principally to differences in preservation rather than to original variation.
 This well-defined species is widespread and abundant in the Culebra formation. It occurs in sandstone, principally in the upper part of the Culebra and in the transition zone between the Culebra and Cucaracha formations. Like other Culebra fossils, most of the specimens have some calcareous sandstone adhering to them or are otherwise poorly preserved. The type, of intermediate size, was collected from pebbly sandstone in the Paraiso region. Its earliest preserved whorls are strongly worn and the others are somewhat worn.
 Turritella caparonis Maury (1925, p. 234, pl. 42, figs. 1, 2), from strata of late early Miocene age in Trinidad, is a related species. It has four equally spaced spirals, the anteriormost (adjoining and obscuring the suture) not quite as strong as the others. The more distinct nodes on the spirals, as compared with T. amaras, are probably the result of better preservation. The two species are similar in growth line. T. amaras may be more closely related to the Oligocene Puerto Rican T. mitchelli Hubbard (1920, p. 137, pl. 22, fig. 3), which has three similarly spaced primary spirals and appears to have a similar growth line. According to the illustration of the imperfect type (and only specimen), it has two strong secondary spirals between the middle and posterior primaries, minor spirals superimposed on the primaries, and fairly strong nodes, particularly on the secondary spirals. Merriam's (1941, pl. 24, fig. 2) Turritella aff. T. altilira, from the Miocene of Colombia, needs comparison with T. amaras.
 T. amaras and its allies represent a minor offshoot from the stock of T. altilira that failed to survive the Miocene.
 Occurrence: Culebra formation (early Miocene), Gaillard Cut, localities 98, 99b, 107, 108b, 108c, 110, 110a, 111a, 111b, 112, 112a, 116.

 Turritella (Torcula) altilira altilira Conrad
 Plate 23, figures 1, 7, 12, 13
Turritella altilira Conrad, Pacific R. R. Expl., v. 6, Geol. Rept., p. 72, pl. 5, fig. 19, 1857 (Miocene, Gatun, Panam). (RePrinted U. S. Geol. Survey Prof. Paper 59, p. 178, 1909.)


 Brown and Pilsbry, Acad. Nat. Sci. Phila. Proc., v. 63, p. 358, pl. 27, figs. 2, 3, 1911 (Miocene, Canal Zone). Olsson, Bull.
 Am. Paleontology, v. 9, no. 39, p. 150, pl. 14, figs. 6, 7, 1922 (Miocene, Canal Zone). Hodson, idem, v. 11, no. 45, p. 45, pl. 26, fig. 1, pl. 28, fig. 3, pl. 29, fig. 1, 1926 (Miocene, Canal Zone). Oinomikado, Geol. Soc. Japan Jour., v. 46, p. 620, pl. 29, fig. 2, 1939 (Miocene, Colombia). Merriam, Calif.
 Univ. Dept. Geol. Sci. Bull., v. 26, p. 44, pl. 24, figs. 3, 4, 1941
 (Miocene, Canal Zone).
 Turritella gabbi Toula, K. k. Geol. Reichsanstalt Jahrb., Band 58,
 p. 695, pl. 25, fig. 5, 1909 (Miocene, Canal Zone).
 Turritella altilira urumacoensis Hodson, Bull. Am. Paleontology,
 v. 11, no. 45, p. 44, pl. 26, figs. 4, 7, pl. 27, figs. 3-7, 10, 1926
 (Miocene, Venezuela).
Not Turritella altilirala Conrad (error for T. altilira), Gabb,
 Acad. Nat. Sci. Phila. Jour., 2d ser., v. 8, p. 341, pl. 44, figs.
 9, 9a, 1881 (Miocene, Costa Rica;= T. sapotensis Brown and Pilsbry). Grzybowski, Neues Jahrb., Beilage-Band 12, p.
 645, pl. 20, fig. 7, 1899 (Miocene, Pera; subsp. of T. altilira). Not Turritella altilira Conrad, Brown and Pilsbry, Acad. Nat.
 Sci. Phila. Proc., v. 64, p. 503 (list), 1913 (Miocene, Culebra Cut, Canal Zone; subsp. of T. allihra). Spieker, Johns Hopkins Univ. Studies in Geology, no. 3, p. 59, pl. 2, fig. 12, 1922 (Miocene, Peri; subsp. of T. altilira). Anderson, Calif.
 Acad. Sci. Proc., 4th ser., v. 18, no. 4, p. 118, pl. 17, figs. 4, 5, 1929 (Miocene, Colombia; subsp. of T. altilira). Marks Bull. Am. Paleontology, v. 33, no. 139, p. 99, 1951 (Miocene,
 Ecuador; subsp. of T. altilira).
 Large, slender, strongly bicarinate. Protoconch small, bulbous, consisting of about 1% whorls. End of protoconch marked by gradual appearance of anterior primary spiral, which rapidly enlarges on first sculptured whorl. Posterior primary spiral appearing on latter part of third or on fourth sculptured whorl, slowly enlarging until on sixth to tenth sculptured whorl it generally is as stong as anterior spiral Even, however, on intermediate whorls of some specimens anterior primary is larger. Unequal minor spirals appearing between primaries on sixth to eighth sculputured whorl. Almost as soon as they appear they are noded (at first microscopically), and a few whorls later nodes appear on primaries. Primary spirals of late whorls flangelike and strongly noded. Posterior primary wider than anterior, generally unequally doubled by partial coalescene of an original strong minor spiral lying in front of it. Minor spirals between primaries conspicuously noded; one minor spiral generally stronger than others. A wide, but low and moderately noded, minor spiral adjoins anterior suture. Minor spirals absent between posterior primary and suture. Wellpreserved specimens show microscopic spirals over entire whorl, including primaries. On last whorl, or a little more, of mature shells, nodes subdued, widely and irregularly spaced, and growth line emphasized at irregular intervals. Minor spiral adjoining anterior suture of spire whorls emerging on base of body whorl as a stong spiral. Remainder of base sculptured with very weak minor or microscopic spirals fading out to-


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