350 Notes on Geological Specimens presented to the Museum. 



taken as types. There can be little doubt that it belongs to the 

 family of the Monticuliporidm, so it may yet take its place with 

 other respectable polysyllables. 



The late Dr. Bishop, of Calne, found some specimens a few years 

 ago, and through his kindness the late Mr. H. Cunnington was able 

 to present a second example to the Museum. 



A COPKOLITIC FllESHWAlEH LiMESTOXE, TiSBUKY. 



During a visit paid to the Vale of Wardour in company with 

 Mr. Prestwich and the late Prof. Edward Forbes, in the year 1851, 

 I ol)served amongst the Freshwater limestones of the Purljeck beds 

 of Tisbury several layers of stone consisting chietiy of minute, 

 oVilong, calcareous l)odies of uniform size and shape, about Im. in 

 length. We were at a loss to account for tliese peculiar and 

 uniform forms. 



Some months afterwards, using a large glass vase for growing 

 Valisneria, the interior of it was, as is usual, soon covered with 

 confervie, and on this growtli nuich carbonate of lime was deposited 

 from the very hard water with which tlie vessel was supplied. To 

 keep down this incrustation, the well-known remedy was applied, 

 some freshwater snails, Li/mncea, &c., were introduced, and they 

 duly fed on the conferva', leaving the surface of the glass clear, 

 but witli traces of their toothed tongues in a distinct pattern all 

 over it. The calcic carbonate thus accidentally taken in with tlieir 

 food was excreted liy these creatures in the form of elongated 

 pellets, which in tlie course of the season accumulated at the 

 bottom of the vase to the depth of nearly half-an-inch. Their 

 close resemblance to the curious forms discovered in tlie Purbeck 

 beds was obvious ; and 1 would suggest that a consideraljle portion 

 of the freshwater limestone strata of Tisbury, Chicksgrove, &c., in 

 South Wilts, and doubtless of other localities of the same geological 

 date, are due to the deposits of the molluscs altove-mentioned. 



