EXPLANATION OF PLATE I. 
Figure 1.—Pinnixa cylindrica Say, (p. 546;) male, enlarged four diameters. 
2.—Pinnotheres ostreum Say, (p. 546;) male, enlarged four diameters. 
3.—Panopeus depressus Smith, (p. 547;) male, natural size. 
4,—Platyonichus ocellatus Latreille, (p. 547 ;) male, slightly reduced in size. 
(All the figures were drawn by J. H. Emerton.) 
