GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 As in the Gatun Lake district, the bulk of the Bohio formation consists of nonmarine boulder conglomerate. At the continental divide the upper part of the formation includes thin lenses of algal-foraminiferal limestone. In the Quebrancha syncline, northwest of Madden basin, the Bohio is made up of graywacke grit, the basal part of which includes marine siltstone. In the northern part of Madden basin the Caimito formation overlaps the Bohio.
 The Gatuncillo formation evidently rests on an uneven surface of the basement complex. Reeves and Ross (1930, p. 18, pl. 5) mentioned and mapped a small outcrop of dioritic rock near the head of Rio Azote Caballo, just south of the present south shore of Madden Lake. This outcrop evidently is the top of a basement hill or ridge, on the sides of which the Gatuncillo is overlapped by the Caimito. Practically pure quartz sandstone in the upper part of the Gatuncillo is exposed along the road from Casa Larga to Laguna, near locality 13-the only locality where such sandstone was observed in the area covered by plate 1.
 Pacific coastal district east of Panamd City.-In the Pacific coastal district east of Panama' City, the Gatuncillo formation is overlapped by the Bohio formation. The Gatuncillo reappears farther east in the valley of Rio Bayano, 45 kilometers east-northeast of the eastern border of plate 1 (Terry, 1956, p. 32).

 DESCRIPTION OF TERTIARY MOLLUSKS
 The formal description of species is held to a minimum. Lengthy descriptions almost invariably include matter at the generic level which is of no value in the discrimination of species.
 The following terms are used for type material of species:
 Type: A specimen selected by the describer as the namebearer of a species. Also known as holotype.
 Paratype: A specimen showing a feature, or features, not
 shown by type. Also used by others for any specimen, other than type, on which the description of a species is
 based.
 Syntype: A specimen in a lot of two or more on which a
 species is based, but none of which was selected by the
 describer as the name-bearer. Also known as cotype.
 Lectotype: A syntype subsequently selected as the namebearer.
 Neotype: A specimen, from the same locality and horizon,
 selected as the name-bearer to take the place of destroyed
 or lost type material.
 Topotype: A specimen from the same locality and horizon
 as the name-bearer.
 Terms used for types of genera are as follows:
 Orthotype: Type by original designation.
 Monotype: Type by monotypy. Also known as haplotype.
 Tautotype: Type by tautonymy.
 Logotype: Type by subsequent designation.


 Adoption of the preceding terms for the types of J genera, which have the advantage of brevity, was prompted by Iredale's (1939, p. 223) usage in his Greatt Barrier Reef report. Monotype, however, has beei substituted for haplotype. Iredale's usage was base{ on Jordan's, who in turn picked up terms from Cooke,k but also added one of his own. Those interested in thy origin and varying usage of the terms in the preceding: two lists will find definitions and citations in Frizzell's useful "Terminology of types" (1933). It is entirely appropriate to use the term "type" for a species and a genus. There can be no confusion: the type of a species is a specimen, whereas the type of a genus is a species.
 The following new subgeneric names are proposed:
 Aepystoma, subgenus of Teinostoma, Vitrinellidae.
 Type: Teinostoma (Aepystoma) andrium Woodring, n.
 sp., Gatun formation, Miocene, p. 70. Gender neuter."
 Diaerecallus, subgenus of Teinostoma, Vitrinellidae.
 Type: Teinostoma (Diaerecaluns) .sychnum Woodring, ni.
 sp., Gatun formation, Miocene, p. 71. Gender mascul
 line.
 Hapalorbis, subgenus of Solariorbis, Vitrinellidae.
 Type: Circudus liriope Bartsch, Recent, Gulf of California, p. 75. Gender masculine.
 Hypterita, subgenus of Neverita, Naticidae, Polinicinae.
 Type: Natica helicoides Gray, Recent, Baja California
 to Perd, p. 92. Gender feminine.


GASTROPODS


I


 Family TROCHIDAE
 Trochids are rare in the Tertiary formations of the Canal Zone and adjoining parts of Panama. Each of the two species of Calliostoma herewith described is represented by two specimens. In addition three othet trochids are recognized: a minute "Margarites" from the middle part of the Gatun formation; an exfoliated apical fragment sculptured with nodose spirals, evidently a calliostome, also found in the middle part of the Gatun formation; and an incomplete impression, probably a calliostome sculptured with weakly noded spirals, from the Toro limestone member of the Chagres sandstone. Each of these three trochids is represented by only one specimen.

 Subfamily MARGARITINAE
 Genus?
 "Margarites" species
 Minute, very thin-shelled, outline naticid, whorls rapidly enlarging. Protoconch consisting of a smooth naticoid whorl. End of protoconch marked by fine closely spaced axial and spiral threads. Both sets of threads gradually become more widely spaced and on later part of penult they disappear, the early part of the penult bearing a sutural thread, a thread on the shoulder, and widely spaced retractive axial threads


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