EXPLANATION OF PLATE XIII 



Isotelus iowensis, Owen, page 48. 



Fig. 1. View of the inner surface of the test, showing position of the facial 

 suture. Mus. No. P 11241. X 1. 



Fig. 2. Ventral view of a cephalon in the paleontological collection of the State 

 University of Iowa, showing form and position of the hypostoma and sutures. X ^7. 



