MARINE CRUSTACEANS. 697 
macrurous. A moveable antennal scale often present. Third pair of maxillipeds usually 
narrow. Anomura. 
2. Carapace fused with epistome at the sides and nearly always in the middle. Last thoracic 
sternum fused with the rest, its legs often like the others. Abdomen brachyurous (small, 
straight, symmetrical, bent under the thorax, showing no traces of any other function than 
that of reproduction, and without biramous limbs on the 6th segment). Never a moveable 
antennal scale. 3rd pair of maxillipeds usually narrow. Brachyura'. 
Key to the tribes of the reptant Macrura. 
I. Carapace fused at the sides to the epistome. Rostrum small or wanting (except Palinwrellus). 
Inner lobes of 2nd maxillae and Ist maxillipeds reduced. An appendix interna on some of 
the abdominal limbs, at least in the female, but the exopodite of the last pair without sharp 
suture. Body often depressed. 
1. Carapace gripped by first abdominal segment alone. First joint of antenna not fused with 
epistome ; a scale present on this limb. All the legs, except sometimes the last pair, chelate; 
the first longer than the rest. Unbranched limbs on the first abdominal segment. Tail-fin 
not softer behind than before, without sutures. Telson pointed. Eryonidea. 
1) 
Carapace gripped between a lobe on the lst abdominal segment and a knob on the side 
of the last thoracic segment. First joint of antenna fused with epistome; no scale on this 
limb. None of the legs much longer than the rest or, except sometimes the first pair, 
chelate. No limbs on the Ist abdominal segment. Tail-fin divided by indistinct sutures 
into a soft hinder half and a harder front half. Telson roughly squared behind. Scyllaridea’. 
II. Carapace free from the epistome. Rostrum of good size. Inner lobes of 2nd maxillae and 
Ist maxillipeds not reduced. No appendix interna, but the exopodite of the last abdominal 
limb divided by a suture. Body subcylindrical. [Carapace gripped by first abdominal segment 
only. Ist joint of antenna free. A scale present. First three legs chelate, first pair the 
longest. Telson firm, squared, often sutured. ] Nephropsidea. 
Key to the tribes of the Anomura. 
I. End-joints in 2nd to 4th legs curved and flattened. First pair styliform or subchelate. [Tail-fin 
not adapted for swimming. Abdomen bent under thorax. Rostrum small or wanting. 3rd pair 
of maxillipeds carry no mastigobranchs. | Hippidea’. 
II. End-joints in 2nd to 4th legs not curved and flattened. First pair not styliform, rarely 
subchelate. 
1. 6th abdominal limb adapted for swimming (except in TZhalassina where it is styliform. 
Pleura usually well developed. Abdomen symmetrical. 
a. Body depressed. A pleurobranch to the last leg. Often a transverse suture on the 
telson. Abdomen more or less bent under the thorax, Galatheidea. 
6. Body compressed. No pleurobranch to the last leg. No transverse suture on the telson. 
Abdomen straight. Thalassinidea*. 
1 For a classification of the Crabs, with keys, see above, articles which deal with them. 
vol. 1. pp. 426 ff. 3 For a classification of this group, with keys, see Ann. 
2 Keys to the families of these groups will be givenin the Mag. N. H. (7), xu. 
