734 



titJD '• THETIS " SCIENTIFIC RESULTS. 



Key to the Australian Species of the Gends Zygometra. 

 a^. II [ Br series mostly, or entirely, 2. 



b^. 2 III Br series developed on each post-radial series, internally ; 

 tliirty arms ; thirty-tive or fewer cirrus segments (? N. Aus- 

 tralia) Z. comata. 



h'^. Numerous III Br series developed on each post-radial series, 

 externally as well as internally ; forty or more arms ; forty 



or more cirrus segments (X. Australia) ...Z. elegans. 



a^. Ill Br series mostly, or entirely, 4 (3 4-4). 



6^. 4 division series ; proximal pinnules very large and stout {N. 



Australia) ..Z.microcUscus. 



h'^. 3 division series ; proximal pinnules slender {N. Australia) 



...Z. multiradiata. 



Key to the Australian Species of the Genus Ampiiimetka. 

 a^. More than ten arms ; the proximal pinnules with strong lateral 



processes on the segments ((i>//eeH.sto?tfZ ; N. W . Australia). ..A. variipinna. 

 a''. Ten arms ; the proximal pinnules smooth. 



b^. Cirri very stout, all the segments much broader than long, 



subequal (N. W. A ustralia) A. milberti. 



b'^. Cirri moderately slender, at least the proximal segments 



longer than broad [Queensland) A. discoidea. 



Key to the Australian Species of the Genus Heterometra. 



•fl^, 35-55 cirrus segments, the outer half with moderately developed 

 spines ; lower pinnules not carinate ; thirty-eight arms (Queens- 

 land) H. nematodon, 



a^. 20-25 cirrus segments, the outer with long sharp spines ; lower 

 pinnules strongly carinate ; eighteen or less arms [Queensland) 

 H. htngalensis. 



Key to the Australian Species of the Genus Dichrometka. 

 a^. Lower pinnules considerably larger on the outer arms of each 

 post-radial series than on the inner, and very slender ; 20-30 

 cirrus segments, the outer with small spines ; 32-43 arms [Queens- 

 land). D. tenera.. 



a'^. Lower pinnules appijoximately of equal size on all the arms. 

 b^. Pa longer than Pg. 



C-. P2 not greatly larger than P3 ; thirty-eight arms [Queens- 

 land).. D. reginoi. 



c^. P^ not much longer than P.^ ; forty-one arms [Thursday 



Island) D. gyges. 



6^. Pj and P3 about equal in length ; 35-40 cirrus segments, the 



owtev Sf^iny [Queensland) D. articulata. 



Key to the Australian Species of the Genus Oligometra. 



a\. P^ much the largest pinnule on the arm ; the whole animal 



delicate and slender. Pg with large processes on the lower 



segments [Queensland a,i\ A N.W. Australia) 0. carpenteri. 



a^. P^ the longest pinnule ; the whole animal is stout. 



6^. Cirri XX, 2 0; two dorsal transverse ridges on each cirrus 

 segment ; genital pinnules not expanded [N. W. Australia, 

 Thursday Island, Queensland) O. adeoncR. 



