One of these grottoes made of twenty-seven specimens of Planorbis contortus

Anonyme, « How we began shell-collecting », Recreative science; a record and Remembrancer of Intellectual Observation, vol. 2, Londres, Groombridge & Sons, 1861, p. 36.

It was in one of these mill-streams we were first delighted by finding the cases of the caddis-worm ( Phryganea), made of shells many of them still alive, and not much the worse for their durance . One of these grottoes is made of twenty-seven specimens of the compact little Planorbis contortus (each fastened by its upper surface) and one example of P. marginatus (Fig. 1). Some coutained small bivalves (cyclades), and others afforded examples of a minute landsnail, Vertigo palustris, the first of the kind we had seen. Sir C. Lyell describes a freshwater limestone in Auvergne, wholly made up-as he believes-of similar « indusia » of the case-worm, incrusted and cemented together with calcareous tufa.