1 8 Pratt, Bipolar TJteory. 



Further, Polychajta, described in the preceding paper: 

 Species : — 



Gom'ada norvegica. 

 A renicola daparcdii. 

 Bispira maricE, and, 



doubtfully, Polydora polybrancJiia. 



Genera : — 

 Eteone. 

 Promenia. 



Polydora (species also extra-tropical). 

 Bis pit a „ „ „ 



? Atitolytns almost exclusively extra-tropical, but 

 has been taken in the Red Sea — probably an 

 escape from Mediterranean. 

 The following northern species of Polychseta are very 

 nearly related to southern species. 



Southern. Northern. 



1. Travisia kerguelensis related to T. forbesi. 



2. Scoloplos kerguelensis „ „ ^". armiger. 

 The following northern species of Gephyrea are very 



nearly related to southern species. 



Northern. Southern. 



3. Echiuriis tuiicinctus related to E. chilensis. 



4. Priapulus typicus. ,, „ P. atistralis. 

 To the "four littoral cases of bipolarity " acknowledged 



by Ortmann we must, then, add 28 cases — 22 of species, 

 and 6 of genera — making a total of 32 littoral bipolar 

 forms, or 19 of species and a total of 29 cases if we exclude 

 the three species Polydora polybranchia, Scalibregma in- 

 flatum and Phascolosoma viargaritaceuni. The two latter are 

 typically littoral forms, but each has been once taken in 

 sub-surface waters, Scalibregma off New Zealand in 700 

 fathoms, and Phascolosoma off Norway in 300 fathoms. 



