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 Mmticuliporidce, so it may yet take its plaee with 

 other respectable polysyllabies. 



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

 ago, and through his kindness the late Mr. II. ( iinnington was able 

 to preseul a second example to the Museum. 



A COPKOLITIC FRESHWATER LIMESTONE, TlSBURY. 



During a visit paid to the \*ale of Wardour in company w ith 

 Mr. Prest wich and the late Prof. Edward Forbes, in the year L851, 

 1 observed amongsl the freshwater Limestones of the Purbeck beds 

 of Tisbury several layers of stone consisting chiefly of minute, 

 oblong, calcareous bodies of uniform size and shape, aboul Lm. in 

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

 uniform forms. 



Souk 1 months afterwards, using a large glass vase for growing 

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

 conferva', and on this growth much carbonate of lime was deposited 

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



keep down this incrustation, the welbknown remedy was applied, 

 some freshwater snails. Li/mima, \c, were introduced, and they 

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

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

 over if. The calcic carbonate thus accidentally taken in witli their 

 food was excreted by these creatures in the form of elongated 

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

 bottom of the vase to the depth of nearly half-andnch. Their 



close resemblance to the curious forms discovered in the Purbeck 

 beds was obvious; and I would suggest that a considerable portion 

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

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

 date, are due bo the deposits of the molluscs above-mentioned. 



