30 



Eyes and antennules almost always {nomoJodromia is the only exception) 

 retractile into common orbito-antennulary pits, the lower wall of which is formed 

 about equally (1) by the basal joint of the antennule itself, (2) by the basal joint 

 of the antenna, and (3) by a sub-orbital spine or dentiform lobe. 



These orbito-antennulary pits very often show traces of a sub-division into 

 two fossae, one for the antennule the other for the eye — the boundary between 

 the two fossa? often being a tooth or a sort of fold in the upper margin of the 

 " orbit." 



Bye of the ordinary form, situated at the end of a short stout eye-stalk, the 

 basal joint of the eye-stalk being inconspicuous. 



Epistome triangular, its apex in close contact with the deflexed tip of the 

 front. Vault of the palate of good depth. 



External maxillipeds iisually opercular, sometimes subpediform. 



Fingers of the chelipeds generally short, stout, channelled along their 

 opposed surfaces, and strongly calcified in their distal half. 



Sternum of the female traversed longitudinally, in part or in almost all of 

 its extent, by a pair of special grooves that sometimes end in special tubercles. 



The abdomen of both sexes consists of seven separate segments. Very 

 often a pair of small lateral plates — the rudiments of the 6th pair of abdominal 

 appendages — is intercalated between the Gtli and 7th somites. 



The gill-plumes vary in number from 20 to 14 on either side, and are either 

 trichobranchife or phyllobranchife. 



Many of the species are protected by a commensal Sponge or Ascidian, or 

 by an empty valve of a Lamellibranch shell, carried over the back. 



The Dromiidea are divided into three subfamilies which are distinguished as 

 follows : — 



Synoims of the families of Dromiidea. 



Tlie last two pairs of legs are reduced in size, subdorsal, and 

 preliensile : — 



1. Lateral borders of carapace ill defined. Tlie appendages 

 of the 6th abdominal somite are not in any way represented. 

 Epipodites are present on the chelipeds and next two pairs 



of legs. Gill-plumes 19 or 20 on either side, trichobranchia^ Homolodromid^. 



2. Lateral borders of carapace well defined. Tlie appendages 

 of the 6tli abdominal somite are represented by a pair of 

 plates intercalated between that somite and the telsoii. 

 Epipodites may be present on tlie chelipeds, but not on any 



■ ; of the legs. Gill-plunies 14 or 10 on either side, phyllo- 



branchia? ... ... ... ... ... Dromid.k. 



