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Species / Tylostoma Allisoni

Tylostoma Allisoni

Stromboidea


Original diagnosis:

  • "Large Tylostoma with shell moderately ovate-elongate, spire high, last whorl with very narrow varix on left side, inner lip with thin callus, outer lip thick, and growth lines mostly orthocline, but prosocline on subsutural and basal areas."

Original description of Tylostoma allisoni by Squires & Saul, 2004:

  • "Shell large (up to 123 mm in height), ovate-elongate, and thick. Shell height/shell diameter ratio approximately 2. Spire high, approximately 35% of shell height. Pleural angle approximately 55°. Protoconch missing. Teleoconch whorls seven. Suture moderately impressed. Whorls rounded and smooth; last whorl with slight shoulder. Specimens with slightly decorticated shells showing one prominent, very narrow varix along peripheral margin on left side of last whorl at exactly 90° to aperture. Anomphalous. Aperture oval, radial, approximately 46% of shell height. Inner lip with thin callus. Outer lip thick. Columella smooth. Growth lines mostly orthocline but prosocline on subsutural and basal areas, with greatest deflection on last whorl periphery."

Locus typicus: Shore of Punta China, approximately 2 km S of mouth of Rio de Santo Tomás, northwestern Baja California State, Baja California Peninsula, Mexico

Stratum typicum: Alisitos Formation, upper member, late Aptian, lower Cretaceous

Holotype: UCMP no. 33732

Paratype: CAS no. 69105

Etymology: Named for Edwin C. Allison, in recognition of his important work on mollusks of the Alisitos Formation

References:

  • Squires R.L. and Saul L.R., 2004. Uncommon Cretaceous naticiform gastropods from the Pacific Slope of North America. The Velliger 47(1-2):21-37

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