176 IOWA ACADEMY OF SCIENCE 



Occurrence: Calvin's "Spirifer pennatus" beds, uppermost 

 part of the Wapsipinicon stage (Fayette breccia), Devo- 

 nian; near Independence, Iowa. 



Specimens in the paleontological collections of the University of 

 Iowa. 



Geological Laboratories 

 State University. 



EXPLANATION OF PLATE V C. 

 Atrypa reticularis (Linnseus). 



Figure 1. Pedicle view showing the strong development of the mar- 

 ginal lamella?. Note the fine ribs on the shell and the wrinkling of 

 the lamellar surface. 

 No. 600, x J 



Figure 2. Same specimen. Posterior view. 



Figures 3, 4. Lateral and pedicle views of a young specimen showing 



the fine ribs and the "decidedly lenticular" form mentioned by 



Calvin. No. 601, x {- 



Figures 5, 6. Lateral and brachial views of a nearly mature example 

 showing the initiation of greater convexity in the brachial valve. 

 Note the rather weakly developed varices on this and the preceding. 

 No. 602, x | 



Figures 7, 8. Brachial and lateral views of an old individual. Note 

 the strong sub-equally spaced varices from which the lamellae have 

 been broken off. 

 No. 603, x ' 



