GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 Height 0.9 mm, diameter 1.5 mm (type).
 Type: USNM 561324.
 Type locality: 185 (USGS 8383, Caribbean coast, west of Rio Miguel, Panama), upper part of Gatun formation.
 This subspecies is based on two specimens from the upper part of the Gatun formation. Though the spirals flanking the periphery are narrower and lower than those of "Circulus" liriope, the sculptural pattern is the same, suggesting close relationship. As indicated by the name, however, alliance with the smaller Hapalorbis from the middle part of the Gatun formation is thought to be closer. Both Solariorbis hyptius proper and S. hyptius anebus have a depressed outline and very narrow umbilical wall, whereas "Circulus" liriope is less depressed and has a wider umbilical wall.
 A Pliocene species from Ecuador, "Pseudorotella" lens Plisbry and Olsson (1941, p. 47, pl. 9, fig. 2; 194552, p. 51, 1952) has the same sculptural pattern as Solariorbis hyptius anebus and "Circulus" liriope, but has a heavy callus facet almost closing the umbilicus and is sculptured with two spiral threads above the periphery, The Recent Panamic "Vitrinella" seminuda C. B. Adams (Pilsbry and Olsson, 1945-52, p. 278, pl. 27, figs. 3, 3a, 3b, 1945; p. 51, 1952) lacks spirals above the periphery.
 Occurrence: Upper part of Gatun formation (middle and late Miocene), eastern area, locality 173, western area, locality 185.
 Genus Episcynia Mdrch
M6rch, Malakozool. Bldtter, Band 22, p. 155, 1875. Type (monotype): Architectonica (Episcynia) inornata (d'Orbigny)
 (Solarium inornatum d'Orbigny), Recent, West Indies.
 In the western Atlantic Episcynia ranges from North Carolina to Brazil, and in the eastern Pacific from Santa Cruz Island, Calif., to Peru. Miocene species from Florida and the Caribbean region are the earliest known.
 Episcynia megalia Woodring, n. sp.
 Plate 18, figures 4, 8
 Large, thin-shelled, whorls 5. Suture shallow, located on peripheral carina of preceding whorl, even at peristome. Peripheral carina minutely and irregularly roughened by exaggerated growth wrinkles. Similar growth wrinkles adjoin suture on later part of body whorl. Umbilical half of base and umbilical wall sculptured with more strongly emphasized growth wrinkles. Upper half of umbilical wall also sculptured with two narrow spiral threads that disappear near peristome. Umbilical border sharply angular.
 Height 2.7 mm, diameter 5.3 mm (type).
 Type: USNM 561325.


 Type locality: 138 (USGS 16909, Transisthmian Highway, 1.6 kilometers northeast of Canal Zone boundary, Panama), lower part of Gatun formation.
 Episcynia megalia, which is based on one specimen from the lower part of the Gatun formation, is the largest Episcynia so far described. It is most closely related to two species living in the eastern Pacific: E.nicholsoni (Strong and Hertlein) (1939, p. 241, pl. 22, figs. 2-4; Panama) and the closely allied E. bolivari Pilsbry and Olsson (1946, p. 11, pl. 1, figs. 6-8; Colombia and Peru; Pleistocene, western Panami). On both Recent forms the carina is exposed on the later whorls of the spire. E. nicholsoni evidently is more depressed than E. megalia, and E. bolivari has a slight angulation on the body whorl above the periphery.
 E. naso (Pilsbry and Johnson) (Pilsbry, 1922, p. 379, pl. 37, figs. 5, 5a), the only other described fossil species from the Caribbean region (Miocene, Dominican Republic and Jamaica), has strong regularly spaced, serrations on the peripheral carina.
 Occurrence: Lower part of Gatun formation (middle Miocene), locality 138.
 Family RISSOIDAE
 Subfamily RISSOINAE
 Genus?
 "Alvania" aff. "A." epulata (Pilsbry and Johnson)
 Minute, rapidly enlarging. Protoconch very large for size of shell, consisting of 2% rapidly enlarging smooth whorls. Remaining 2% whorls sculptured with closely spaced axial ribs (17 on body whorl), between which are closely spaced spiral threads. Base sculptured with three wider and more widely spaced spirals. Outer lip varicose, its interior inaccessible.
 Height 1.2 mm, diameter 0.7 mm.
 Two minute specimens, both found by T. F. Thompson in the Gatun formation, are the only rissoids. They evidently are conspecific and are closely allied to "Rissoa" epulata Pilsbry and Johnson (Pilsbry, 1922, p. 384, pl. 34, fig. 5), a Miocene species from an unknown locality in the Dominican Republic. That species is narrowly umbilicate. The specimen from the lower part of the Gatun formation is immature and has a narrow umbilical groove, but the mature specimen from the upper part of the formation, of approximately the same dimensions as the type of "Rissoa" epulata, is completely nonumbilicate.
 Rissoids more or less similar to the Gatun species are generally referred to the genus Alvania (Risso, 1826, p. 140; logotype, Nevill, 1884 [1885], p. 105, Alvania europea Risso= Turbo cimex Linn6, Recent, Mediterranean). The type of Alvania is four times as large, and has a relatively much smaller protoconch, coarser sculpture, and lirations on the interior of the outer lip.


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