S. P. Woodward, « How we began shell-collecting » Recreative Science : A record and Remembrancer of Intellectual Observation, vol II, Londres, Groombridge and Sons, 1861, p. 36.

It was in one of these mill-streams we were first delighted by finding the cases of caddis-worms (Phryganea), made of shells many of them still alive, and not much the worse for their durance. One of cese grottoes is made of twenty-seven specimen of the compact little Planorbis contortus (each fastened by its upper surface) and one example of P. marginatus (Fig. 1). Some contained small bivalves (Cyclades), and others afforded examples of a minute land-snail, Vertigo palustris, the first of the kind we had seen.

Sir C. Lyell describes a fresh-water limestone in Auvergne, wholly made up-as he believes-of similar « indusia » of the case-worm, incrusted and cemented together with calcareous tufa.