EXPLANATION OF PLATE V. 
FiGuRE 20,—Caprella geometrica Say, (p. 567;) lateral view, enlarged about three 
diameters. 
21.—Spheroma quadridentata Say, (p. 569;) dorsal view, enlarged five diam- 
j eters. 7 
22.—Idotea ceca Say, (p. 569;) male; dorsal view, enlarged three diameters. 
23.—Idotea irrorata Edwards, (p. 569;) male; dorsal view, enlarged two 
diameters. 
24,.—Idotea robusta Kroyer, (p. 569;) male; dorsal view, enlarged two diam- 
eters. 
(Fignres 20, 21, 23, and 24, were drawn by J. H. Emerton; figure 22 by O. Harger.) 
