Clasnijication of the Decapod Crustaceans. 477 



Key to the Families of the Paguridea. 



I. Abdomen straight or twisted. Carapace firm 

 aud more or lesa compressed in the fore part, 

 soft in the hinder part, at least at the sides. 

 Fourth le^rs unlike third. Rostrum almost 

 or quite wanting-. Sixth abdominal limb 

 present. 



1. Abdomen macrnrous and symmetrical, with 



all the limbs present. Trichobraiichiate. Pylochelidae. 



2. Abdomen more or less unsymmetrical, some 



of tlie limbs lost. Generally phyllo- 

 branchiate. 

 i. Antenual scale well developed (thorn- 

 like). First antennae with stalk of 

 moderate lenpth and flagella ending iu 



a tiiament. Marine forms Paguridae. 



ii. Antennal scale reduced. First antennae 

 with very long stalk and flagella ending 



bluntly. Land forms Coenobitidae. 



II. Abdomen bent under thorax. Body crab- 

 like. Carapace firm all over. Fourth legs 

 like third. Ko-strum spiniform. Sixth ab- 

 dominal appendages lost Lithodida. 



Key to the Subfamilies of the Paguridse. 



I. Third maxillipeds approximated at bise. 

 Chelipeds equal or subequal, or the left much 

 the larger PagurintB. 



II, Third maxillipeds wide apart at base. Right 



cheliped usually, left never, much the larger. Eupagurina. 



Key to the Suhfamilies of the Lithodidae. 



I. Third to fifth abdominal segments imperfectly 



calcified. Rostrum short and broad Hapalogastrinee . 



II, Third to fifth abdominal segments well calci- 

 fied. Rostrum generally narrow and pointed. Lithodinte. 



Key to the Suhtribes of the Brachyura. 



I. Mouth-field (endostome) prolonged forwards 

 to form a gutter. [Last pair of legs normal 

 or abnormal. Female openings generally 

 sternal. First abdominal limbs of female 



wanting. Gills few.] OXYSTOMATA. 



II. Mouth-field roughly square, 



A. Lastpair of legs abnormal, dorsal. Female 



openings coxal. First abdominal limbs of 



female present. Gills usually many .... DKOMIACEA. 



B. Last pair of legs normal, rarely reduced, 



not aorsal, except in Valicus and Pteno- 

 pla.c. Female openings sternal. First 

 abdominal limbs of female wanting. Gills 

 few BRACIIYGXATIIA. 



