4IO 



PLATE V. 



I, 2, 3, 4. Orthis rogata; (i) ventral view of a large specimen; (2) 

 lateral profile, and (3 and 4) interior of two dorsal valves showing the 

 muscle scars. 



5, 6, 7. Orthis macrior; lateral, dorsal and anterior views. 

 8, 9, 10. Orthis corpulenta ; dorsal, ventral and lateral views of an 

 average mature specimen. 



II, 12, 13. Orthis tersa ; (14) interior of a dorsal valve; (12) dorsal 

 view and (13) lateral view. 



14, 15, 16, 17. Orthis minnesotensis ; (14) ventral of an average speci- 

 men; (15, 16, and 17) ventral, dorsal and posterior views of a large indi- 

 vidual. / 



18, 19, 20, 21. Orthis petrae; dorsal, ventral and posterior of an aver- 

 age specimen, and (21) dorsal of a younger (?) form. 



22, 23, 24. Strophomena inquassa; interior of a dorsal valve, a longi- 

 tudinal section and dorsal view, from three specimens. 



