334 Notes on Margaritana margaritifera (Linne). 



Characteristic of this species is, that it lives in swiftly- 

 running brooks on the hills, the waters of which are rather 

 poor in lime. When, by any accident, the epidermis is des- 

 troyed, the anterior margin and umbones are often dissolved 

 by the water and the animal is gradually destroyed, and finally 

 there only remains the chitin of which the epidermis consists. 



When extraneous bodies enter into the mussel between the 

 shell and mantle, the latter is irritated, and the animal 

 secretes ' mother of pearl ' around the irritant bodies, and in 

 this way the pearls are formed. According to Lionel E. Adams, 

 Suetonius says that Caesar was partly attracted to Britain 

 by the reports of pearls found there, and Pliny states that he 

 covered a buckler with them, which he dedicated to Venus 

 Genetrix. Tacitus mentions a theory current in his time 

 that the dull reddish colour of our pearls was due to their being 

 collected from cast-up shells instead of being gathered from 

 living shells from the bottom of the sea ; but he adds, with 

 characteristic dry humour, that the fault probably lay in the 

 pearls themselves, as otherwise his avaricious countrymen would 

 have been sure to discover the best methods of obtaining them. 



Schroter tells in his work * how the Chinese produce 

 genuine pearls. He says that they introduce into every mussel 

 a diminutive ball made of mother of pearl, after which operation 

 the mussel is deposited in the river beds. After some years, 

 the mussel is again fished up, when every ball is found to be 

 coated with a new layer of mother of pearl. 



Big ball-shaped clear pearls are the most valuable, and the 

 price is fixed according to size. Pearl fishing was formerly 

 carried on in many parts of Europe, but it does not pay as, 

 according to Clessin, one hundred mussels must be examined 

 in order to obtain a single pearl, and only one of eighteen 

 pearls can be used ; a few times, however, big finds have been 

 made, for instance in Donegal and in the Conway. 



Mr. H. A. Allen sends us a ' Catalogue of Types and Figured Specimens 

 of British Cretaceous Gasteropoda preserved in the Museum of Practical 

 Geology, London, reprinted from Summary of Progress of the Geological 

 Survey for 191 5. 



In the Memoirs and Proceedings of the Manchester Literary and Philo- 

 sophical Society (Vol. LXL, pt. 1) Mr. H. Bolton has a paper on ' The 

 " Mark Stirrup " Collection of Fossil Insects from the Coal Measures of 

 Commentary (Allier), Central France.' 



Mr. Charles Bailey favours us with a copy of his interesting paper 

 ' On the Contents of a Herbarium of British and Foreign Plants for 

 presentation to the Victoria University of Manchester, reprinted from 

 Vol. LXL, part 2, of Memoirs and Proceedings of the Manchester Literary 

 and Philosophical Society, Session 1916-7. 



* Die Geschichte der Feussconchylien, Halle, 1779, p. 178. 



