Subgenus Umbonis

Original Description

"SUB-GENUS 9. UMBONIS.

SHELL TURRET-SHAPED, LOWER TOOTH CENTRAL, MORE THAN THREE TIMES AS LONG AS HIGH. STRIATIONS, GREATLY ENLARGED, BULGING AND WIDENED IN THE MIDDLE, THESE AND THE INTERSPACES BETWEEN THEM ARE CROSSED BY FINE, TRANSVERSE DEPRESSIONS. APERTURE CON­TRACTED, WITH A SLIGHTLY FLANGING MARGIN. UMBILICUS, CLOSED.

This is the most strongly marked group of Strophais which I have seen and is characterized by the turret-shaped shell, large, wide apart striations which are enlarged in the middle, giving each whirl a very abruptly bulging appearance.

But the most remarkable character of all, is the transverse lines or depressions which cross the shell everywhere, excepting on the first three whirls. This must be an old type of Strophia, or rather this singular feat­ure must be one of the most primitive, for we find in many shells, even of widely different species, a tendency to revert toward this. See remarks under S. dimidiata. There are but two known species of this interesting sub-genus." Maynard, 1896:28.

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