PLATE XIX. 



Mesotkypa Selkirkensis (page 162). 



Figure 1. Transverse section of a portion of a specimen of this species, magnified 

 fifteen times. 

 M la. Longitudinal section of ». portion of a specimen, also magnified fifteen 

 times. 



Rafinesquina lata (page 172). 



Figure 2. View of a specimen with most of both valves preserved, shewing the dorsal 

 valve and part of the ventral. The hinge areas of both valves, and 

 the cardinal extremities, restored in outline from other specimens. 



,1 2a. Outline of a transverse section of the same in the median line, shewing 

 the relative convexity of the ventral valve and concavity of the dorsal 

 valve. 



.1 26. Portion of surface markings of the dorsal valve of the same, magnified 

 three times. 



II 3. An imperfect ventral valve, with coarse corrugations on the visceral disc. 



II 4. Unusually perfect cast of the interior of a ventral valve of a specimen from 

 the Red River valley in Manitoba, loaned by the Smithsonian Insti- 

 tution, and shewing most of the marginal outline. 



II 5. Portion of the surface markings of a ventral valve, magnified three times. 



