GAMMARIDEA. 827 



ingly agile ; while the Gammaridae are water species, and generally 

 less active in their movements. 



The several families above mentioned may be characterized as 

 follows : — 



Fam. I. Dulichid^e. — Habitu Caprelloideae. Corpus lineare, epimeris 

 obsoletis. Pedes 6 postici longi, subprehensiles. Abdomen 5-arti- 

 culatum. 



Fam. II. Chelurhle. — Corpus fere cylindricum, epimeris mediocribus. 

 Abdomen abnormale, segmentis 4to 5toque coalitis et oblongis, 

 stylis inter se valde dissimilibus. 



Fam. III. Corophidjs. — Gressoriae, pedibus partim lateraliter porrectis. 

 Corpus plus minusve depressum, sive latum sive lineare, epimeris 

 perbrevibus, interdum obsoletis. Abdomen forma appendicibusque 

 normale. Antennae saepe pediformes. 



Fam. IV. Orchesttd^e. — Saltatoriae, pedibus nullis lateraliter por- 

 rectis. Corpus compressum, epimeris magnis. Abdomen appen- 

 dicibus normale. Antennae non bene pediformes. Styli caudales 

 Imi 2dique biramei ; 3tii simplices, brevissimi et ultra 2dos non 

 prolongati. Mandibulae non palpigerae. Maxillae lmae palpo sive 

 parvulo et 1-articulato sive obsoleto instructae. 



Fam. V. Gammarhxe. — Saltatoriae vel natatoriae ? pedibus nullis late- 

 raliter porrectis. Corpus saepius compressum, raro subdepressum, 

 epimeris sive magnis sive parvis. Styli caudales laxiores, duobus 

 ultimis oblongis saepiusque ultra 2dos prolongatis, raro simplicibus. 

 Mandibulae saepissime palpigerae. Maxillae lmae palpo 2-3-arti- 

 culato (rarissime 1-articulato) instructae. 



The homologies of the parts of the shell forming the surface of the 

 head in the Gammaridea, are considered in our general remarks on 

 the family Orchestidae. 



The most difficult point in the study of the Gammaridea, as in the 

 Caprellidea, is that of ascertaining sexual distinctions. Males and 

 females are often very diverse. The former may have the antennae 



