266 THE VOYAGE OF H.M.S. CHALLENGER. 



The single species of Bathyoncus is from far south. 



Polyca/rpa has two representatives in the northern hemisphere, and three in the 

 southern tropical zone, while the remaining seven species are from the southern temperate 

 regions. 



Of the seven genera of the Ascidiidse, two, Corella and dona, are confined to the 

 northern hemisphere, and three, Abyssascidia, Corynascidia, and Pachychlcena, are 

 purely southern. 



Ascidia is only represented by one species in the northern hemisphere, the remaining 

 ten species being confined to southern temperate regions. None of the Challenger 

 Ascidiidse occur in the tropics. 



Hypobythhis has one species in the northern hemisphere and one in the southern, 

 both at considerable distances from the equator. 



The Clavelinidse are almost equally represented in the two hemispheres, having two 

 species north of the equator and three to the south. Clavelina has one species in each 

 temperate zone, and is not represented at intermediate latitudes. Ecteinascidia, finally, 

 has one species [Ecteinascidia turbinata) in the northern temperate region, while the 

 remaining two are from the southern tropics. 



