Prionocyclus macombi Meek 1876, found in the middle of the Juana Lopez Member of the Mancos Shale. This specimen is 335mm dia.  These are probably a new species because the shell on typical P. macombi usually becomes smooth at some later stage, these have strong fold like ribs throughout growth, intermediate between P. macombi and P. wyomingensis, they also have the beginings of an outer row of ventro-lateral tubercles.

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