GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 The importance of the sculpture of the early whorls and the growth line in a study of the affinities of turritellas was emphasized by Merriam in his monograph of fossil turritellas from the Pacific coast of North America. His term "growth-line angle" (Merriam, 1941, p. 59) is adopted for the angle between the axis of the shell and a line extending from the posterior end of the growth line to the anterior end on spire whorls, or to the apex of the forward bend, if such a bend is present near the anterior suture.
 Merriam pointed out that among the several hundred described species of Turritella, groups of closely allied species are as distinctive as groups of species in other families-groups that are given generic and subgeneric rank in other families. Nevertheless he was reluctant to assign superspecific names to the groups of species lie recognized, as suitable material for consideration of many of the superspecific names proposed for turritellids was not available to him. He therefore grouped his species into stocks named for a typical species (Merriam, 1941, p. 33-55). At an earlier date Guillaume (1924) classified European Tertiary species in groups, also named for a typical species. Merriam's stocks, however, are more restricted than Guillaume's groups and afford a much better basis for a satisfactory classification. Guillaume relied on the growth line, ignoring the development of the sculpture and other features.
 Though no exhaustive study has been attempted, only one subgenus of turritellas from the Canal Zone and adjoining parts of Panama appears to have a suitable name: Torcula; in fact, two names (Torcula and Bactrospira) are available for that subgenus, which corresponds to Merriam's T. altilira stock.
 Subgenus? (?Guillaume's T. hybrida group, in part)
 Turritella cf. T. carinata Lea
 Plate 14, figure 2
 Moderately large, moderately slender. Whorls slightly concave, the profile modified by a spiral forming a basal carina immediately adjoining anterior suture. Remainder of late whorls apparently smooth; remainder of intermediate whorls apparently smooth' or sculptured with a low spiral at anterior third. Poorly preserved early whorls show a spiral at about anterior third, but no other sculpture apparent. Growth line not known.
 Height (incomplete, 7+ whorls) 41.5 mm, diameter 16 mm (figured specimen).
 The figured specimen and fragments consisting of several intermediate and late whorls are silicified fossils from the Gatuncillo formation in the Rio Casaya area. The basal carina suggests affinity with the Claiborne (middle Eocene) species Turritella carinata (Palmer, 1937, p. 189, pl. 24, figs. a, 6, 8, 9, 12). The last few


whorls of some large specimens of T. carinata have no macroscopic spirals other than the basal carina, like the figured fossil from Panama. On other large specimens of T. carinata, however, the last few whorls have one to several additional spirals. Though the figured specimen reaches a greater diameter than T. carinata, even the last whorl tightly clasps the preceding whorl,, whereas the last few whorls of large shells of T. carinata gradually withdraw from the carina. T. carinata has microscopic spiral lineation, but such sculpture would not be reproduced by the granular silica of the fossils from Panama. The early whorls of T. carinata are sculptured with three spirals; the growth-line sinus is very deep and the growth-line angle very narrow.
 The middle Eocene Peruvian T. bosworthi Woods (Woods and others, in Bosworth, 1922, p. 80, pl. 8, figs. 8-10) is more strongly carinate.
 T. carinata evidently represents, in part, Guillaume's T. hybrida group (Guillaume, 1924, pp. 286-290).
 Occurrence: Gatuncillo formation (middle Eocene), Rio Casaya area, locality 38.

 Subgenus?
 Turritella cf. T. collazica Maury
 Plate 16, figure 13
 Large, late whorls rapidly enlarging. Whorls slightly concave, the profile dominated by a wide swollen basal carina occupying anterior third, or a little more, of whorl. Other sculpture obscure or absent. Sculpture of early whorls and growth line unknown.
 Height (incomplete, 4+ whorls) 56 mm, diameter (exaggerated by crushing) 25 mm (figured specimen).
 The basal limestone of the La Boca marine member of the Panama formation on Rio Masambi yielded a poorly preserved crushed Turritella characterized by a wide swollen basal carina. The Oligocene Puerto Rican T. collazica has a similar basal carina (Maury, 1920, p. 51, pl. 8, fig. 5). According to Maury's illustration, the basal carina bears a groove and the remainder of the whorl is sculptured with six low spiral threads.
 A fragment from the Culebra formation at locality 5857, listed as Turritella sp., resembles the La Boca species, but its preservation is too poor to permit identification.
 Occurrence: Liniestone at base of La Boca marine members of Panama formation (early Miocene) Rio Masambi, locality 123.
 Subgenus? (?Merriam's T. buwaldana stock)
 Turritella ef. T. samanensis Olsson
 Moderately large, slender. Whorls slightly convex or flat, sculptured with about 10 subequal low spirals. On at least some intermediate and late whorls the basal


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