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JOURNAL OF CONCHOLOGY. 



Vol. 12. OCTOBER, 1909. No. 



ON THE FORMER OCCURRENCE OF UNIO (MARGARITANA) 

 MARGARITIFER Linne IN THE RIVER THAMES. 



By J. WILFRID JACKSON, F.G.S., and A. .S. KENNARD, F.G.S. 



(Read before ihc Society, May 12th, 1909). 



The following" account of a hitherto unrecorded discovery of shells 

 of the above species in the bed of the Tliames will no doubt be of 

 great interest to many conchologists, especially as the species has not 

 yet been taken in a living state in the south-east of England. 



About twenty years ago a number of large U7iios was dredged from 

 the bed of the Thames at Mortlake. Some of these shells were taken 

 by the workmen to the well-known dealer, Mr. G. Lawrence, of 

 Wandsworth, from whose hands they passed into those of Professor 

 W. Boyd Dawkins, and several valves were afterwards placed in the 

 Manchester Museum. Further dredging operations were carried on 

 in the same neighbourhood about nine years ago, and again a large 

 number of the shells was obtained. The workmen picked out the 

 largest specimens, and they passed through the same dealer's hands, 

 and eventually became the property of Dr. Frank Corner, F.G.S. , of 

 Poplar, who kindly placed them at our disposal. 



Mr. Lawrence informs us that the shells were dredged well out in 

 the river, and at a fair depth in the gravel bed, not near the surface. 

 The valves are of an exceedingly large size, the greater number 

 measuring six inches in length and three inches in breadth. Two ex- 

 amples measure six and a half inches by three inches, and six and a 

 quarter by three and a quarter respectively. They are extremely well 

 preserved, periostracum and hinge ligament being present in many 

 cases. They appear to be by far the largest examples of this species 

 hitherto recorded. A very large series of specimens from numerous 

 localities, both British and continental, has been examined and 

 measured, but no individuals have been found to approach the Thames 

 examples in size. Most of the specimens appear to be the var. 

 si fill aid Lam. 



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