ZOOLOGY, 



STRAY NOTES ON THE PEARL MUSSEL. 

 By WILLIAM JAPP, F.S.A. 



I HAVE sometimes wondered why the black pearl mussel 

 (Unio margaritiferus Turton), (Alasmodonta margaritifervs 

 Gray), is not to be found in the bed of the Isla from its rise in the 

 Forest of Caenlochan, at the head of Glenisia, Forfarshire, down 

 to the confluence of the Isla with the Dean, a distance of about 

 1 8 miles. The reason may be found in the fact that the bed of 

 the river for this distance is stony ; the river is usually rapid, and 

 there is an absence of smooth and slow-moving water, which, with 

 a gravelly bottom, forms the best habitat for the pearl mussel. 

 The watershed of the Isla, from Caenlochan Forest to the conflu- 

 ence with the Dean, represents a mountainous country with many 

 streams running down from glens, which all help on a sudden 

 rainfall to fill the main bed in great volume ; and it is to be 

 feared that an experiment lately tried by me, (October, 1881), 

 may not be suited to the nature of the river bed. The experiment 

 was that of introducing the mussel into the Isla at a point well up 

 the river where the channel is full and comparatively deep. 



There is a romance about the early history of the pearl mussel, 

 which gives a charm to everything connected with it. Pearls have 

 been allied with the name of Britain from the very earliest times ; 

 and one Roman historian has attributed Caesar's expedition to 

 Britain to his desire to search for and to own pearls. Pliny con. 

 firms this statement by affirming that Julius Caesar presented a 

 breastplate covered with British pearls to Venus Genitrix, and 

 hung it in her temple at Rome. There are several other references 

 which add to the charm, and strengthen the inference that the de 



