]p. 3

Niagara Group

Polydilasma turbinatum, Hall,
Pal. of N.Y. Vol. 2 p. 112 pl. 32 fig. 2

Turbinate or clavato-turbinate,
usually short; outer surface nearly smooth,
or transversely somewhat rugose; cell deep,
gradually decending from the margin
half way to the centre, and then deep-
ining almost vertically; rays numerous,
thin, becoming complicated before
reaching the centre, often apparently
crenulate on the weathered exterior;
transverse septa irregular, and some-
times nearly or quite obsolete. --
Varying in form

L 1.7. D 1.0