PLATE LXI. 



Page. 

 Fig. 1. BilUngseUa coloradoensis 450 



1. Ventral valve, from Gallatin Range, x 2. 



la. Dorsal valve, from same locality as fig. 1. x 2. 

 16. Interior of dorsal valve, from same locality as fig. la. x 3. 

 lc. Interior of ventral valve, from same locality as fig. 1. x 3. 

 Id. Cast of interior of ventral valve, Gallatin Range, x 3. 

 Fig. 2. Orthis (!) sandhergi 452 



2. Ventral valve, x 3. 

 2a. Dorsal valve, x 3. 



26. Interior of dorsal valve, x 6. 

 2c. Interior of ventral valve, x 3. 

 2d. Enlargement of fig. 2c. x 12. 

 Fig. 3. Orthis rcmnicha » 451 



3. Interior of dorsal valve, x 3. 

 3a. Interior of ventral valve, x 3. 



470 



