ASTACIDEA. 515 



beyond beak, very slender ; the flagellum reaching as far forward as 

 the anterior legs. The large' hand is longer than twice its width. 

 Either side of the beak there is a slight ridge running longitudinally 

 for a short distance from the front edge. The postero-lateral piece of 

 the carapax has the anterior margin denticulate. The postero-dorsal 

 piece is subacute behind, and has two distinct transverse sutures, 

 besides another more anterior less distinct. 



SUBTRIBE II. ASTACIDEA. 



THE division Astacidea is identical with the " Familia Macroura 

 Astacina" of De Haan, in its extent and subdivisions, except that we 

 exclude the Thalassinidea, which De Haan places in the same sub- 

 division with Astacus, and we do not add the Megalopidea, as they 

 appear to have closer relations with the Anomoura. The following 

 are the families adopted : 



1. Antennce externce squamd basali non instructce. Pedes antici monodactyli. 



Fam. I. SCTLLARID^;. Carapax valde depressus, marginibus laterali- 

 bus sat tenuibus, carapace lateraliter subito inflexo. Antennas 

 externae laminatae, breves. Sternum trigonum. 



Fam. II. PALINURID^E. Carapax subcylindricus, lateraliter late ro- 

 tundatus. Antennae externaa basi subcylindricae, longae. Sternum 

 trigonum. 



2. Antennce externce squamd basali instructce. Pedcs antici didactyli. 



Fain. III. ERYONIDTE. Carapax non oblongus, depressus, lateribus 

 subito inflexis, abdomine multo angustiore. 



