GASTROPODS: TROCHIDAE TO TURRITELLIDAE


 Variation affects the strength of the spirals and therefore the whorl profile. Though late whorls are typically bicarinate, the bicarinate outline is somewhat obscured on some specimens by weakening of one or both primaries, or by development of posterior minor spirals that are almost as strong as the posterior primary (pl. 15, fig. 16).
 Turritella cf. T. caleta occurs in the marine member of the Bobio(?) formation. It is represented by numerous fragments and immature specimens, or shell tips, in collections from Vamos Vamos and Trinidad Island, and was found near Palenquilla Point. Apparrently it is related to the Oligocene Peruvian T. caleta Olsson (1931, p. 79, pl. 12, figs. 9, 11, 12, 15), but the ;early sculpture of that species is unknown. The late whorls of T. caleta have a weak posterior primary spiral.
 The bicarinate outline and growth line suggest rela.tionship to T. altilira Conrad. That suggestion, however, is not supported by the sculpture of the early whorls. The bicarinate outline and growth line also suggest relationship to T. olssoni Clark (Clark and Durham, 1946, p. 25, pl. 23, figs. 14-16, 22), a late Eocene Colombian species, which has less strongly beaded late whorls. T. olssoni was claimed to be an early member of the T. altilira group. Specimens that show the early sculpture, available through the kindness of J. Wyatt Durham, substantiate that claim, the earliest sculptured whorls bearing an anterior spiral, a weaker posterior spiral appearing later. T. cf. T. caleta therefore is not related to T. olssoni.
 Occurrence: Marine member of Bohio(?) formation (late Eocene or Oligocene), Gatun Lake area, localities 40, 40a, 40b, 40d, 41, 42, 42c.
 Subgenus Torcula Gray
 Gray, Proc. Zool. Soc. London, p. 155, 1847. Type (orthotype): Turbo exoletus Linn6, Recent, Florida and
 West Indies.
 The subgenus Torcula is characterized by an anterior spiral on the earliest sculptured whorls, an intermediate sculpture of two widely spaced spirals, typically a similar mature sculpture of two primary carina-forming spirals, and also a deep growth-line sinus and a narrow growth-line angle. The intermediate sculpture of the type species is weak, five or six whorls sculptured 'with two weak spirals following the first two whorls sculptured with a stronger anterior spiral. The intermediate sculpture of T. altilira and its close allies is much stronger.
 Most of the lots of T. exoleta in the U. S. National Museum collections are from depths of 35 to 85 fathoms. A few lots, however, were dredged at shallower depths; one lot from Conch Key, Fla., at a depth of 1 to 5 feet. As orally pointed out by R. T. Abbott, it is remarkable
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that a species almost unobtainable except by dredging was available to Linn6.
 Bactrospira Cossmann (1895-1924, pt. 9, p. 129, 1912; type [orthotype], Turritella perattenuato Heilprin, Pliocene, Florida) is available as a name for a minor group under Torcula, including T. altilira and its close allies. T. altilira has more rapidly enlarging early whorls than T. perattenuata. Eurytorus Gardner (1926-47, p. 596, 1947; type [orthotype], Turritella mixta Dall, Miocene, Florida), proposed as a section of Torcula, has the growth line and early and intermediate sculpture of Torcula. The whorls enlarge so rapidly, however, and on mature whorls two or three original secondary spirals are so strong that subgeneric rank may be justified.
 T. amaras is by no means a typical species of Torcula in plan of mature sculpture. It is somewhat comparable to Eurytorus in divergence from the basic pattern of Torcula, but diverges in a different direction.
 Turritella (Torcula?) amaras Woodring, n. sp.
 Plate 16, figures 4-7, 10
 Large, rapidly enlarging. Whorls typically flat; suture typically obscured by overhanging anterior spiral. Intermediate and late whorls of some specimens carinate at the anterior spiral, the suture being exposed. Sculpture consisting of three strong subequal primary spirals. Earliest preserved whorls sculptured with two spirals, anterior one at about anterior third of whorl, posterior one at about posterior third; anterior spiral slightly stronger. These spirals are middle and posterior spirals of subsequent whorls. Anterior spiral, adjoining suture, appearing at early stage and gradually increasing in size. Middle and posterior spirals farther apart than middle and anterior, the middle spiral lying in front of middle of whorl. One to three weak secondary spirals generally present between middle and posterior primaries, and between posterior primary and suture. Well-preserved shell surfaces show microscopic spiral strike. Primary and secondary spirals of some whorls obscurely noded by growth lines. Growth-line sinus deep, the apex at about middle of whorl between middle and posterior spirals; growth-line angle narrow.
 Height (incomplete) 47 mm, diameter 14.5 mm (type, a specimen of intermediate size). Height (incomplete, 3+ whorls) 43 mm, diameter 24.5 mm (figured fragment of large specimen).
 Type: USNM 561373.
 Type locality: 116 (USGS 5853, west side of Gaillard Cut, Canal station 1863, Canal Zone, Culebra formation.
 The only important variation affects the whorl profile. Carinate whorls owe their profile to loose clasp-


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