26 PEARLS AND PEARLING 



5. The Distomid of Kelly is very similar to the Dis- 

 to mid of Osborn. However, they are not so common and 

 are not usually associated with sporocysts or cercariae. 

 It does not produce a salmon colored stain or any other 

 stain, usually. This distomid is frequently found in the 

 thicker shelled mussels such as Lampsilis ventricosus, L. 

 Hgamentinus, Obovaria circulus, and especially in Quad- 

 rula tuberculata and Unio gibbosus. 



It is said that most of the dorsal baroques which are 

 found by pearl hunters are formed through the activities 

 of this parasite. 



6. Bucephalus polymorphus, von Baer is a common 

 parasite which affects many mussels. It has been found 

 to be very dangerous to mussels, and is probably to be 

 regarded as a parasite. 



8. Leeches were found quite frequently on the inside 

 of the shells of the anadonta, and are probably para- 

 sites. 



9. Ata.v ypsilophorus was a common parasite and was 

 particularly common on anadonta. It has been suggested 

 that the eggs of the Atax may lead to the formation of 

 pearls ; but this has not been proved. 



As a rule the anadontas and other thin shelled mus- 

 sels are more heavily parasited than the thick shells, and 

 parasites are more abundant in shallow, warm and quiet 

 pools than in rivers. 



There has been a theory in regard to the origin of 

 pearls in which a grain of sand or small pebble was said 

 to be the nucleus of a pearl. In some localities this 

 theory is accepted as a fact, yet from the experiences 



