Page:Walcott Cambrian Geology and Paleontology II.djvu/94



Body elongate, cylindrical. Anterior end with a circle of plates about it (as preserved as casts on the rock). Posterior end slightly contracted, mouth terminal. Anus unknown but probably terminal. Tentacles and interior structure unknown.

Genotype.—Mackencia costalis, new species.

The stratigraphic range and geographic distribution are the same as for Laggania (p. 52).

This rare form was first placed among the annelids when the collection was unpacked, but with the study of the material preparatory to photographing the different species it was removed to the holothurians. The cylindrical form, circle of plates, and banded appearance at once suggested a fossil resembling Synaptula hydriformis (Lesseur) but without its beautiful tentacles.