. Bulletins of American paleontology. 26 Bulletin 348 Table 5. — MeasurementsofCymhiles laevigatus(J. de C. Sowerby, 1827). All measurements are in mm. specimen DM- WW- no. AX D UD U WH' HWD WH WHD WH GSC 98579 11 2 GSC 98580 4 4 100 GSC 99018 4 MEAN 96 ST. DEV. 7 4 Remarks. — Fanninoceras has been considered a syn- onym oiRadstockiceras Buckman, 1918, by Donovan and Forsey (1973), Donovan et al. (1981), and Meister (1986) but not by th
. Bulletins of American paleontology. 26 Bulletin 348 Table 5. — MeasurementsofCymhiles laevigatus(J. de C. Sowerby, 1827). All measurements are in mm. specimen DM- WW- no. AX D UD U WH' HWD WH WHD WH GSC 98579 11 2 GSC 98580 4 4 100 GSC 99018 4 MEAN 96 ST. DEV. 7 4 Remarks. — Fanninoceras has been considered a syn- onym oiRadstockiceras Buckman, 1918, by Donovan and Forsey (1973), Donovan et al. (1981), and Meister (1986) but not by those workers who have actively studied eastern Pacific Lower Jurassic faunas (Frebold, 1967; Imlay, 1968, 1981; Hillebrandt, 1981, 1987; Smith, 1986; Smith and Tipper, 1986; Thomson and Smith, 1992). The reasons for its retention are based primarily on morphology but also on stratigraphic range. Fanninoceras undergoes a marked change in mor- phology during its ontogeny (Text-figs. 27 and 28). Early whorls are depressed, with a rounded venter and commonly ornamented with either coarse or fine rib- bing depending on the species. At this stage the um- bilical wall is low and grades evenly into the flanks. As the ribbing disappears, the whorls become com- pressed with a sharp venter, an undercut umbilical wall, and an acutely angled umbilical shoulder. Frebold (1967) has pointed out that the external suture of Fan- ninoceras is wider than in Radstockiceras and the lat- eral lobe consequently occupies a position nearer the middle of the flank. Radstockiceras is a Lower Pliensbachian genus that ranges as high as the Davoei Zone in northwest Europe. The exact age oiFanninoceras has long been uncertain but it is now known to be characteristic of the entire Upper Pliensbachian with the first occurrence in beds that correlate approximately with the upper Davoei Zone (Smith et a!., 1988) and its last occurrence (one locality) in the lowest Toarcian of Chile (Hillebrandt and Schmidt-Efl
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