8o PEARLS AND PEARLING 



The "mucket" yields many slugs and baroques and 

 some very fine pearls. 



The Quadrula pustulosa, or "warty-back," or "pimple," 

 is shown in Fig. 15, about one-third natural size. This 

 shell is well known among the pearl hunters. It is found 

 in most rivers, but not often found in lakes. 'This is a 

 very good button shell, and in some instances is consid- 

 ered almost as good as the "niggerhead." The nacre is 

 almost always white, with a good luster. It is variable, 

 sometimes being very smooth and rather flat, while in 

 other" streams the shells are very rough and round and 

 consequently of less value as button material. 



Another shell which is very similar and is sometimes 

 thought to be the same shell is The Quadrula tuber cu- 

 lata, or "purple warty back." This variety often grows 

 to be larger than The Quadrula pustulosa, but is not -valu- 

 able for buttons on account of its dull purple nacre. It 

 is not found in large beds like some varieties, but is usu- 

 ally mixed with other shells. This variety is mentioned 

 because it is an important shell in the pearl hunting in- 

 dustry. The "purple warty-back" is the most liable to 

 infection, by distomids, of all the heavy shelled varieties. 

 It is a great producer of slugs and baroques and is very 

 likely to produce fine pearls. All the slugs, baroques, or 

 pearls found in this variety are purple and dark purple, 

 corresponding to the color of the nacre of the shells. 



The Tritogonia tuberculata is a very odd shell. It is 

 commonly called "deerhorn," or "buck-horn," or "pistol- 

 grip," or "fan-tail," and is shown in Fig. 16 about one- 

 third natural size. The ones fqund in the upper portion 



