210 



PROCEEDINGS OF THE NATIONAL MUSEUM 



The character of the membranes, spines, and setae on the thoracic 

 legs is given below (for explanation of symbols, see figm-e 1): 



Caudal rami of female and male attached to posterior surface of 

 abdomen. Width slightly more than half length, greater in male than 

 in female. Inner margin setuliferous; distal end with six plumose 

 setae, three from distal margin, one from inner distal corner, one from 

 outer distal corner, one from ventral surface. Setae from distal 

 margin long, from lateral and ventral surfaces short. 



Remarks.- — This is the second known species of the genus. The 

 first, D. curtus, is known only from the tropical and subtropical western 

 North Atlantic. The two species possess general similarities but differ 

 in characteristics such as thoracic leg armature and the shape of the 

 various processes and accessory structures. A list of the major 

 differences between D. curtus and D. bij'urcatus is given below: 



D. curtus (female; male unknown) 



1. Posterior end of cephalothorax cover- 



ing fourth thoracic leg-bearing seg- 

 ment and part of genital segment. 



2. Posterior end of genital segment al- 



most fiat, with two small protrusions 

 of posterior lateral margin. 



3. Genital segment spines (fifth legs) 



jointed, two-parted. 



4. Abdomen attached to ventral surface 



of genital segment, with small lap- 

 pet^like protrusion of outer distal 

 corner. 



5. Postoral process a simple spinelike 



process. 



6. Third thoracic leg exopodite process 



simple. 



D. bif meatus (female) 



1. Part of fourth thoracic leg- 



bearing segment visible be- 

 hind cephalothorax. 



2. Posterior end of genital seg- 



ment bilobed, without pro- 

 trusions. 



3. Genital segment spines (fifth 



legs) not jointed. 



4. Abdomen attached to posterior 



surface of genital segment, 

 without small lappet-like 

 protrusion of outer distal 

 corner. 



5. Postoral process bifurcate. 



6. Third thoracic leg exopodite 



process bifurcate. 



