/ / : CONTENTS. XIU 



Class VI. Tunicata. {Hetero-hrancJiiata) 331 



Fam. I. Ascidiadce. — Ascidium, Molgula, Cynthia, 



Pelonsea, Chelyosoma, Boltenia 337 



Fam. II. Clavellinida. — Clavellina, Perophora, Syn- 



tethys 339 



Fam. III. Botryllidce. — Botryllus, Botrylloides, Di- 

 demnium, Eucoelium, Leptoclimim, Distomus, Dia- 

 zona, Polyclinum, Aplydium, Sidnyum, Amorcecium, 



Parascidium, Synoecmm, Sigillina 340 



Fam. IV. Fyrosomidce. — Pyrosoma 343 



Fam. V. BaljpidcB. — Salpa, Doliolum, Appendicularia 344 



CONCLUSION. 



CHAPTER I. 



Numerical Estimate. — Living and fossil species; animal- 

 feeders and vegetable-feeders ; fresh- water, marine, and 

 land-shells ; shell-bearing and naked mollusca 347 



CHAPTER II. 



Geographical Distribution. — Land provinces ; marine 

 provinces. — Specific areas; specific centres. — Generic 

 areas ; sub-generic areas. — Boundaries ; influence of 

 climate. — Origin of provinces 349 



Marine Provinces. — Arctic genera; tropical genera; 

 cosmopolitan species 353 



I. Arctic Province 354 



II. Boreal Province : Norway, New England 357 



III. Celtic Province : Britain, Denmark 359 



IV. Lusitanian Province: Portugal, Canaries, 



Madeira, Azores, Mediterranean, Black Sea 361 



V. Aralo- Caspian Province : 364 



VI. West-African Province 366 



VII. South-African Province 367 



VIII. Indo-Pacific Province : Bed Sea, Persian 



Gulf 368 



