This high resolution micrograph may show important features involved in calcareous plate formation within the alveoli that underlie the plasma membrane in Coleps. Densities are seen on the inner alveolar membrane at its corners with septa. These densities are not known at this time in other ciliates and may be involved in calcareous platelet formation within the alveoli or in stabilizing the surface shape. Filamentous material fills the cytosolic space between two densities. Rough endoplasmic reticulum bears prominent ribosomes. Standard glutaraldehyde fixation followed by osmium tetroxide, dehydrated in alcohol and embedded in an epoxy resin. Microtome sections prepared at approximately 75nm thickness. TEM taken on 3/4/69 by R. Allen with Philips 300 operating at 60kV. Neg. 39,900X. The raw film was scanned with an Epson Perfection V750 Pro. This high resolution image is suitable for quantitative analysis. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).