Alonzo Gray, Elements of Geology, New York, Harper, 1860, p. 198.

A very small crustacean Cypris (Fig 80 is a living species of this genus), contributed largely to the formation of the fresh-water marls in Auvergne (see p. 194). With the marls are associated limestones, formed by an aggregation of the indusiae of the Caddis-worms (May-fly). Theese are little tubes coated with small shells, and bits of wood or straw, and remain after the larva have passed into the perfect state. Fig. 81 represents one of these tubes.