GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 the middle part. The acme of the typical form is reached in the middle and upper parts of the Gatun. The typical form is less abundant in the middle part west of the canal than east of the canal, and no form was found in the upper part in the coastal area west of the Canal Zone. Most of the lots collected in the middle part west of the canal are small specimens identifiable only in the unrestricted sense. A mold of a small specimen records the presence of the species in the Toro limestone member of the Chagres sandstone. According to current age assignments, Turritella altilira, in the unrestricted sense, therefore ranges from late Oligocene to early Pliocene; the typical form from late early Miocene to middle Miocene.
 T. altilira and its immediate close allies are widely distributed in the upper Oligocene deposits of Puerto Rico, Antigua, Trinidad, Venezuela, and Panama; the lower Miocene of Haiti, Dominican Republic, Puerto Rico, Anguilla, Brazil, Trinidad, Venezuela, Colombia, Panama', and Costa Rica; the middle Miocene of Jamaica, Dominican Republic, Trinidad, Venezuela, Colombia, Panami, Costa Rica, southeastern Mexico, Florida, Ecuador, and Pertd; the upper Miocene of Trinidad, Venezuela, Colombia, Panama, Costa Rica, the Colorado Desert of southern California; and the lower Pliocene of Panami. Nineteen names have been proposed for forms of the T. altilira group. Some doubtless are superfluous, but many are to be regarded as subspecies of T. altilira; indeed six were described as subspecies or varieties. A study of the stratigraphic and geographic grades would be certain to yield valuable results, but would be a lengthy diversion. Only a few of the described forms combine flange-like, strongly noded primary spirals and a posterior primary wider than the anterior. Nevertheless middle Miocene fossils from southwestern and northern Colombia and Venezuela have flange-like, strongly noded primary spirals, and some have a posterior primary wider than the anterior. They so closely approach the typical form that they are referred to it. That is, the typical form occurs in the central Panama area, along the south border of the Caribbean Sea, and at the south end of the Miocene Atrato Valley strait.
 The T. altilira group reached southeastern United States in middle Miocene time. Gardner's (1926-47, p. 595, pl. 57, fig. 17, 1947) Turritella cf. T. altilira, found in the Shoal River formation of Florida, represents a form of T. altilira, but like many Caribbean forms it lacks flangelike primaries. Merriam's (1941, p. 44-47) Pacific coast T. altilira stock consists of T. inezana Conrad and T. imperialis Hanna. T. inezana appears in the early Miocene of California as a migrant. Though the immediate predecessor of T. inezana has not been recognized, the presence of a subspecies of the


closely related T. altilira in the late Oligocene of PanamS shows that tropical America was a potential reservoir for the lineage leading to T. inezana, as had been inferred. Merriam has pointed out that T. imperialis, of disputed Miocene or Pliocene age (preferably late Miocene) is practically indistinguishable from some forms of T. altilira that lack flangelike primaries. It presumably is to be treated as a subspecies of T.4 altilira.
 T. altilira has living allies in the Caribbean Sea and in the Panamic region: T. exoleta (LinnS) and T. mariana Dall, respectively. Neither closely resembles the typical form of T. altilira. T. exoleta is the type of Torcula.
 Occurrence: Calcareous sandstone(?) member of Caimito formation (early Miocene), Madden basin, localities 77 (T. cf. T. altilira), 80. Alhajuela sandstone member of Caimito formation (early Miocene), Madden basin, localities 88 (T. altilira s. 1.), 89, 92 (T. altilire s. 1.). Lower, middle, and upper parts of Gatun formation (middle Miocene). Lower part, localities 137a, 138a, 139 (T. altilira s. 1.). Middle part, eastern area, localities 141, 142, 143 (T. cf. T. altilira), 146, 147b, 147c, (T. cf. T. altilira), 147e (T. altilira. s. 1.), 147f, 147g, 147h, 150a, 151, 152 (T. altilira s. 1.), 153, 153a, 154, 155, 155a, 155b, 155c, 157, 158, 159, 159a, 160 (T. altilira s. 1.); western area, localities 161c, 161d (T. altilira s. 1.), 162 (T. altilira s. 1.). 162a (T. altilira s. 1.) 165 (T. altilira s. 1.), 166 (T. altilira s. 1.), 168 (T. altilira s.l.), 170a. Upper part, eastern areas, localities 171, 173a, 174, 175, 176, 177, 177c, 177d (T. altilira s. 1.), 178. Toro limestone member of Chagres sandstone (early Pliocene) locality 195 (T. altilira s. 1.). Middle Miocene, Choc6, southwestern Colombia; northern Colombia. Middle Miocene, Falcon, Venezuela.

 Turritella (Torcula) altilira Conrad, subspecies Plate 15, figure 10
?Turriella aff. T. perattenuata praceellens Pilsbry and Brown,
 Mansfield, U. S. Natl. Mus. Proc., v. 66, art. 22, p. 55, pl. 9,
 figs. 7, 8, 1925 (Miocene, Trinidad).
 Moderately large, moderately slender. Primary spirals relatively low, strongly noded. Posterior face of posterior primary slightly concave. Posterior primary wider than anterior, doubled or tripled. Minor spirals between primaries of unequal strength. Sculpture of early whorls unknown. Growth line like that of typical T. altilira.
 Height (incomplete, 5+ whorls) 29.5 mm, diameter 13.3 mm (figured specimen). Height (incomplete, 7 whorls) 41.5 mm, diameter 17 mnm.
 The shell tapers more gently than that of the typical form of Turritella altilira. The most conspicuous difference, however, lies in the features of the primary spirals,


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