42 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 122 



its referral to the genus Disco and the family Aiigaptilidae. Until 

 females are discovered, we will not attempt a family designation or 

 generic description. 



Summary 



Calanoid copepods were identified in 51 samples collected by Be 

 multiple sampler, Isaacs-Kidd midwater trawl, and modified Nansen 

 vertical net at stations located in the western Indian Ocean between 

 the northern Arabian Sea and approximately the subtropical conver- 

 gence. The Be net collections were obtained between 2000 and 

 1000 m, the midwater trawl samples between the surface and a max- 

 imum depth of 3820 m, and the Nansen vertical net samples between 

 2000 and 1000, 3000 and 2000, and 4000 and 3000 m. 



The displacement volumes of the zooplankton and numerical density 

 and size of the copepods collected by the Nansen net were determined 

 and compared to similar collections made in the northeastern Atlantic. 

 In general, the total zooplankton as well as the copepods were more 

 abundant in the 2000-1000 m depth interval than in intervals below 

 2000 m. The mean size of the animals was larger in the 2000-1000 m 

 interval than in the 3000-2000 m interval. The values obtained for 

 the displacement volumes, numerical abundance, and mean size were 

 similar to those in comparable depth intervals in the northeastern 

 Atlantic. 



The greatest number of species in the Nansen vertical collections 

 were found between 2000 and 1000 m (122), a lesser number between 

 3000 and 2000 m (73), and the least number between 4000 and 3000 m 

 (13). This decrease in diversity with increasing depth is similar to 

 that found in the northeastern Atlantic. 



The distribution of 209 species found in the western Indian Ocean 

 was discussed and compared to previous discussions of the geographic 

 distribution of Indian Ocean bathypelagic copepods and to water mass 

 distribution. The very widespread distribution of the bathypelagic 

 species was indicated by the great similarity in species composition be- 

 tween the North Atlantic and western Indian Oceans. Eighty-six 

 percent of the western Indian Ocean species are also present in the 

 North Atlantic. Five typically Antarctic species were found in four 

 samples collected in the southern Indian Ocean near the subtropical 

 convergence. 



Included in the 310 species found are 1 new genus, 17 new species, 

 8 previously unknown males, and 1 previously unknown female. 

 Seventy-eight of the 310 species excluding the newly described ones 

 have not been previously reported from the Indian Ocean. Seven 

 species are apparently known only from the Indian Ocean. 



