538 Wisconsin Academy of Sciences, Arts, and Letters. 



expla:n"atio:n' of plates. 



The figure' numbers in each plate correspond to the number of 

 the case. 



The skiagraphs were taken with dorsal surfaces next tlie 

 plate. The sides are not reversed therefore in the figures, as 

 may be seen bj comparing the photograph and skiagraph in 

 Plate XXXVII. 



Figures 12 and 13 are tracings from skiagraphs since th3 

 plate was broken before good prints were obtained. 



Figure 11 is a drawing substituted by the engraver for an 

 obscure skiagraph. 



