GASTROPODS: TROCHIDAE TO TURRITELLIDAE


ward columellar lip. Growth-line sinus deep, its apex a little behind middle of whorl; growth-line angle narrow.
 Height (incomplete, 6 whorls) 43.5 mm, diameter 17.5 mm (topotype). Height (incomplete 7+whorls), 63 mn, diameter 19 mnm (figured fragment of large specimen). Height (incomplete) 73 mm, diameter 13 1mm (figured almost complete large specimen).
 Type material: Lectotype, Acad. Nat. Sci. Phila. 3513.
 Type locality: Gatu, Canal Zone. Locality of topotype: 150a (USGS 10997, Panama Railroad, high cut about 0.4 mile (650 meters) southeast of Gatun railroad station, Canal Zone), middle part of Gatun formation.
 In February, 1957, Ellen James Trumbull, of the Geological Survey, found at the Academy of Natural Sciences of Philadelphia a poorly preserved 4-whorled specimen of Turritella altilira that was collected by Newberry. It is all that is left of the type lot and is an obligatory lectotype, if not the remains of the 7whorled type illustrated by Conrad. The specimen shown on plate 23, figure 7, was collected close to, if not at, the type locality. In 1855, when Newberry gathered a few fossils on his way to California, Gatun was located on the banks of the Chagres at the west end of the bluffs formed by the Quebrancha Hills. Presumably he found his fossils, including T. altilira, in a railroad cut. In the French literature on the geology of the present Canal Zone, T. altilira is designated T. tornata (T. tornata Guppy= T. guppyi Cossmann, a subspecies of T. altilira).
 The typical form, which has flangelike strongly noded primary spirals, is rare in the lower part of the Gatun formation, but is widespread and abundant in the middle and upper parts in the Canal Zone. The posterior primary is almost invariably wider tian the anterior on late whorls and, with few exceptions, is unequally doubled. Details of sculpture and the degree of whorl constriction between the posterior primary and the suture are variable. No specimens of the typical form are in the U. S. National Museum collections from the lower part of the Gatun fornsation, but T. F. Thompson collected from the lower part three specimens identified as T. altilira altilira. Only one specimen (from locality 138a), however, is really typical. One of the other two-a large specimen from locality 137a--has anterior and posterior primary spirals of equal width. The other (from locality 138a) has a nonflanged posterior primary; that is, it combines characters of the typical form and T. altilira praecellens, with which it is associated. On specimens from about the lower half of the middle part of the Gatun, including strata in the type region, one of the minor spirals in the


concave area between the primaries is stronger and more coarsely noded than the others, and the suture is deeply impressed, as the result of strong whorl constriction (pl. 23, fig. 7). On specimens from about the upper half of the middle part, no minor spiral dominates the others and the suture is not so deeply impressed (pl. 23, fig. 12). On specimens from still higher strata in the upper part of the formation, however, a minor spiral is dominant on about half of the specimens, and most of them have a deeply impressed suture. Shells from a U. S. Geological Survey locality representing the upper part of the formation near Mount Hope (locality 175) have been illustrated by Merriam (1941, pl. 24, figs. 3, 4). Plate 23, figure 13 shows one of the few shells that have a simple posterior primary. On this specimen the posterior face of the posterior primary is not deeply concave. The shell was damaged and repaired while the second preserved whorl was being formed and after the repair the posterior primary is farther from the suture. This specimen therefore is abnormal, but the posterior primary is not doubled preceding the repair.
 Maturity, as indicated by suppression of the nodes, is reached at a diameter of 15 to 20 millimeters. Healed breaks are conspicuous on the body whorl of mature shells and are not unusual on spire whorls. About 200 perfectly preserved shell tips from locality 147b and a considerable number from several other localities show the protoconch and early sculptured whorls (pl. 23, fig. 1).
 In the Canal Zone and adjoining parts of Panami the earliest forms of Trritella altilira appear in the upper Oligocene part of the Caimito formation and in the lower Miocene Emperador limestone member of the Culebra formation; the last in the Toro limestone member of the Chiagres sandstone. The Caimito and Emperador fossils are discussed under the next heading. The earliest occurrence of the typical form is in the lower Miocene part of the Caimito formation in Madden basin. A poorly preserved small specimen from Madden basin, probably from the calcareous sandstone member of the Caimito formation, and molds (including one of a large specimen) from the overlying Alhajuela sandstone member are referred to the typical form. Though some details of the sculpture are partly or completely lacking, the identification is made with considerable confidence, for the primaries are flangelike, and the posterior primary is wider than their anterior and is unequally doubled. Other specimens from the Miocene part of the Caimito formation are too small or too imperfect for identification, other than in the unrestricted sense. A subspecies (or variety), discussed under a separate heading, is represented in the lower part of the Gatun formation and apparently occurs in