390 CRUSTACEA. 



rent canal terminates at the middle, instead of the sides of the front 

 of the buccal area. The area is, therefore, produced and narrowed 

 forward, and the canal is generally a regularly formed channel, 

 covered quite exactly by the inner branch of the first maxillipeds, 

 which branch is narrow and much prolonged. These Crustacea are 

 thus widely different from other Brachyura, and the triangulate form 

 of the buccal area, by which they are distinguished, is the mark of a 

 fundamental distinction. They are brought together by De Haan 

 with the same limits and subdivisions as are here adopted, except 

 that he includes the Raninidae, an Anomoural form ; the Corystidae, 

 a very different type, are excluded. The natural families are as 

 follows : 



1. Appendices maris genitales liasi pedum btor-um ortae. [Via afferens pone regio- 

 nem pterygostomianam ingrediens.^ 



Fam. I. CALAPPID^E. Articuli maxillipedis externi terminales non 

 celati. 



Fam. II. MATUTID^E. Articuli maxillipedis externi terminales celati, 

 3tio triangulate, palpo vix longiore quam articulus 2dus. 



2. Appendices maris genitales sterno ortce. 



Fam. III. LEUCOSHLE. Via afierens aptid angulum palati antero-late- 

 ralem ingrediens. Articuli maxillipedis externi terminales prece- 

 dentibus tecti. Pedes postici ad normam gressorii. 



Fam. IV. DORIPPID^E. Via afferens parte regionis pterygostomianse 

 postica ingrediens. Articuli maxillipedis externi terminales prece- 

 dentibus non celati. Pedes 2-4 postici subdorsales, prehensiles. 



The known genera of living species pertaining to these families are 

 distinguished as follows. 



FAM. I. CALAPPID^E. 

 SUBFAM. 1. CALAPPINJE. Pedes nulli natatorii. 



