MIDLAND UNION PRESIDENT'S ADDRESS. 175 



There are some peculiarities with respect to habitat that are 

 interesting to geologists. Some kinds of freshwater univalves have the 

 faculty of enduring a partial change or difference in their usual habitat 

 which would be fatal to other kinds. Nilsson, the Swedisli naturalist, 

 relates that two species of Limncea described by him, as well as Neritina 

 fluviatilis, live in the Baltic, adhering to sea-weeds, and sometimes at 

 a distance from the mouth of any river. With these live certain 

 marine moUusca, such as the common mussel and cockle, Mya arenaria, 

 and Tellina Balthica. Limnsea is Pulmonobranch, and Neritina is 

 Pectinibrancb. The same peculiarity has been observed in the case of 

 a freshwater bivalve, though not of so permanent a character.* 



The common pond mussel (Anodonta cygnea) is said to live in the 

 River Trent, which is salt at high water. The fresh water, being 

 lighter, forms the upper stratum, while the sea water covers the bed 

 of the river inhabited by the Anodonta. 



Dreissena polymorpha (a kind of mussel which abounds in many of 

 our rivers and canals) M. Marcel de Serres is of opinion was originally 

 marine, from the circumstance of the shells being found in tertiary 

 strata of marine formation. The Russian traveller Pallas (who first 

 discovered or made known this species) described one variety of it as 

 marine, and the other as inhabiting fresh water. 



Planorbis corneus, a well-known and widely-distributed fresh water 

 snail. Lister tried in vain to fix the purple dye yielded by this species 

 in such quantity. 



Monstrosities, or abnormal forms of the MoUusca in this district 

 have been rarely observed, particularly so among the land MoUusca. 



Species of Helix, during the pairing season, are furnished with 

 crijgtaUinc darts, which they shoot at one another. These curious love 

 iceapom have been observed sticking to the bodies of snails after such 

 conflicts. They are contained in a special pouch or receptacle ready for 

 use. In some species each individual has only one of these missiles, 

 in others two, and a few species have none at all. They are not often 

 observed by conchologists. 



ORNITHOLOGY. 



Nottinghamshire, from its diversity of character, is rich in the 

 variety of its feathered tribes. Here are vast tracts of cultivated land 

 giving support to those species which thrive and increase on the fruits 

 of man's labour ; there is also a large area of wood and waste almost 

 in its primitive condition, harbouring other species, which invariably 

 retire before the encroachments of the axe and plough ; many large 

 ponds or lakes, fed by rivulets, giving an asylum to aquatic birds, 

 and the great river Trent, attracting not only the various ducks and 

 waders, the denizens of fresh water, but also those of marine origin, 

 many of which appear to migrate from the south-western coast, 



* Jeffreys, vol, 1, chap. vi. (ci.) 



