EXPLANATION OF PLA7E 13. 



Spirodomus iksignis, Beecher. 



Page 163. 



Fig. 1. A transverse section, taken from about 4o™"i from the anterior end of 



a specimen. 

 Fig. 2. A transverse section, posterior to the middle of the specimen fig. 4. 

 Fig. 3. Id. Section of the conjoined valves, at about the posterior quarter of 



their length. 

 Fig. 4. Id. Ventral aspect of a specimen, which is a partial cast of the interior, 



showing the form of the shell, the muscular scars, pallial line and 



crenulated margins. 

 Fig. 5. Id. The left side of the embedded specimen in the rock, showing the 



expanded crenulate margins of the valves and the pallial line. 



NVaverly group. Warren, Pennsylvania. 



