36 UNIONID^B. 



the hinge not being so strong, nor the teeth so thick, 

 as in U. tumidus. It has been noticed by Mr. Norman 

 to attain, in ponds at Fleckney and Wistow in Leices- 

 tershire, the great size of 4^ inches in breadth and 2^ 

 in length, and to weigh 2 oz. 6 dr. 



It is, however, by no means easy to draw a satis- 

 factory line of separation between this and the last 

 species, which are connected by several intermediate 

 forms, and especially by the U. Philippi of Dupuy. The 

 fact of their inhabiting the same spot shows, at all 

 events, that one of them is not a local variety of the 

 other ; and this ought, I think, to weigh in the scale of 

 specific distinction. Whether one, or both, of these now 

 reputed species have become in course of time permanent 

 varieties or " races " of the same or some other species, 

 may be regarded as an antiquarian (although interesting) 

 question, which does not properly belong to the province 

 of the zoologist. 



Both of these species produce pearls, though of very 

 small size and inferior lustre. A consolidated mass of 

 pearly secretion is sometimes formed inside the right 

 valve near the margin of the posterior side. The shells 

 were used by Dutch painters (from which the specific 

 name of pictorum originated) for holding their colours ; 

 and they are still to be had of any artists'-colourman in 

 this country, containing a preparation of ground gold 

 and silver leaf, for illuminating work, the other purpose 

 having been superseded by palettes. Bouchard-Chan- 

 tereaux calculated that each individual of U. pictorum 

 produced, in the breeding-season of May, June, and 

 July, no less than 220,000 eggs. 



The variety curvirostris bears a strong resemblance to 

 some of the varieties of U. Batavus\ but there is no 

 satisfactory proof of that species having been found in 



