CR USTA CEA—MALA COSTRA CA. 397 



XXVII. Arch^oplax Stimpson. 

 Subquadrangular ; posterior portion very broad, strongly convex, 

 antero-lateral margin with four teeth, the first of which is the 

 largest, and forms the outer angle of the wide orbit; rostrum 

 broad (one fourth the width of the front), truncate, frontal margin 

 with median notched lobe; chelipeds moderate with slender fin- 

 gers; sternum rather broad; expanded anteriorly, and rather flat; 

 abdomen of male rather broad. Miocenic. 



47. A. signifera Stimpson. (Fig. 1695.) Miocenic. 



Length of type 1.6 inches; greatest width 2 inches; posterior 



end 1.5 inches; longitudinal curvature forming a regular arc, as 



Fig. 1695. Archceoplax signifera^ dorsal view of a carapace (drawn so as to show- 

 anterior end and with posterior end foreshortened), ventral view of a male showing 

 sternum and broad post abdomen. (After Stimpson, Bost. Soc. Nat. Hist. Proc, VII.) 



seen in side view the middle height of which is nearly half an 

 inch ; surface smooth, covered with minute punctures, granulated 

 anteriorly, and at the margins ; central region defined by two 

 lunate smooth marks ; last tooth of antero-lateral margin small. 

 Abundant in the Miocenic deposits of Gay Head, Mass. 



Superorder Edriopthalma Leach. 

 Order AMPHIPODA Latreille. 



Body laterally compressed. Abdomen elongate. The three an- 

 terior feet for swimming, the rest directed posteriorly and used 

 for jumping, at least in modern species. Mostly small, aquatic 

 and generally marine. 



Fossil forms are derived chiefly from fresh-water strata. 



