. Bulletins of American paleontology. Qt. Text-figure 55.—Vertically subcylindriLul gastropods withiriwa. D. Marginella apicina. E. Maifiindla lavalleami. \y elongate apertures and apex visible. A, B. Retusa candei. C. Marginella would show some geographic or environmental differ-entiation. It did not, and all specimens were treatedthereafter as one taxon. Several of the compendia of seashells show a formof Modulus in which there are heavy radial ribs on aconvex spire, but in which the periphery is not angu-lated as in the Florida Bay shells. No specimens ofthis form of shell have appeared in
. Bulletins of American paleontology. Qt. Text-figure 55.—Vertically subcylindriLul gastropods withiriwa. D. Marginella apicina. E. Maifiindla lavalleami. \y elongate apertures and apex visible. A, B. Retusa candei. C. Marginella would show some geographic or environmental differ-entiation. It did not, and all specimens were treatedthereafter as one taxon. Several of the compendia of seashells show a formof Modulus in which there are heavy radial ribs on aconvex spire, but in which the periphery is not angu-lated as in the Florida Bay shells. No specimens ofthis form of shell have appeared in our samples. Comparison.—No other comparable rhombic,heavily corded shell appeared in our sampling. Name.—Modulus modulus (Linnaeus, 1758). Biofacies.—This is one of the Ubiquitous Taxa,found in all except the Rocky Shore Biofacies. In afew samples it is the Dominant Taxon, but because itis so common and widespread it is never a Key Taxon. References.—Wannke and Abbott. 1961, pp. 11, fig. J: Abbott, 1974, p. 102, fig.
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