162 WEST COAST SHELLS 



guis. It is found fossil in various localities in the 

 State. Some consider TV. fossata and A^ perguinis 

 as varieties of this species. 



llyanassa obsoleta. Say, the Worn-out Nassa, is 

 a very recent comer to this coast. It is extremely 

 abundant on the Atlantic coast to the south of Cape 

 Cod, being found especially on mud-flats, when the 

 tide is low. In those regions the shell always has a 

 dilapidated appearance, being partly covered with 

 a dismal, mossy growth, and seldom reaching the 

 length of an inch. It came to California, however, 

 probably with young oysters, and settled in San 

 Francisco Bay, on the Alameda side. As frequently 

 happens with immigrants it began to spruce up quite 

 wonderfully. Some specimens were sent me by a 

 lady in Alameda in 1909, who asked for their name. 

 They were so clean and bright and large that I hesi- 

 tated long before I was fully convinced that they 

 were the real "Worn-outs," but such they are now 

 regarded by collectors. They are about the size and 

 shape of Figure 147, but the shell is much thicker 

 and heavier than those of our N. perpinguis. The 

 exterior is dark, with a greenish tinge, while the 

 peristome is brown and glossy, with two white, in- 

 ternal stripes. It would not be strange if they should 

 increase rapidly and become a very common shell. 



