Immanitas is a rudist bivalve genus of the family Caprinidae described by Palmer in 1925. With one possible exception described by Coogan from the subsurface of south Texas, the genus has been reported from only one locality--at Paso del Rio, which is the old ford on the Rio Armeria, just below the village of Periquillos, Colima, Mexico.

The Immanitas bed itself is a single carbonate cycle starting at the base with about 2 m of wackestone, overlain by packstone and perhaps grainstone for a total thickness of 4 m. In the packstone and grainstone the clasts are nearly all rudists, of which there are many giant specimens of species of Immanitas.

The single cycle represents a shoal area in a thick sequence of volcaniclastic rocks, at least part of which are marine. On the high-energy side of the shoal area, to the east, the carbonate bed gives way to dirty quartzarenite. Toward the low-energy side, on the west, the

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shoal grades laterally into black, thin-bedded (8 to 12 cycles per meter), carbonate mudstone.

Part of the length of the boundary between the Immanitas bed and the overlying volcaniclastic rocks has been intruded by diorite. This intrusion resulted in the neomorphism of even the mudstone fillings in the rudists to coarse-grained equant calcite. For this reason, the extent of packstone versus grainstone is difficult to ascertain.

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