320 PALEONTOLOGY OF ILLINOIS. 



In addition to these furrows each valve is marked by about 

 thirty-two longitudinal ridges that are a little wider than the spaces 

 between them. These commence at the dorsal margin near the 

 beak, and when they cross the posterior furrow already described, 

 they are deflected abruptly forward to a right angle with their 

 former course, about two out of every three ending at the anterior 

 furrow, while the others are continuous across that to the anterior 

 border of the shell. 



A small fragment of the shell, attached to the cast, shows that 

 the surface was finely striated obliquely from the beak to the front, 

 and with a good lens the striae are seen to consist of rows of minute 

 granules. 



Dedicated to Mrs. Orestes St. John, by whom this fine specimen 

 was discovered, and to whom I am indebted for the use of it. 



Position and locality : Upper Coal Measures, Shawnee county, Kan. 



