42 



related to P. hippocrepia as the A . branchiata group is related to 

 P. ovalis. This small Actinotrocha is illustrated in Fig. 1 from a 

 specimen which Professor Goodrich kindly lent me. This specimen 

 he obtained from Faro, Messina. 



The two types of Actinotrocha described by Wilson from 

 Chesapeake Bay appear to be related the one to the A. hranchiata 

 and the other to the A. pallida group. His A form is reproduced 

 in Fig. Ij and this probably developes into P. architecta. 



A. Jienseni from the coast of Brazil, measuring only 0-3 mm., 

 with six pairs of tentacles, is a young stage. 



Many species of Actinotrocha have been described from the 

 Indian Ocean and Western Pacific. It is interesting to note that 

 A. ikedae, of Japan, which measures 1 to 1-5 mm and possesses 

 eight pairs of tentacles, is beheved to be the larva of P. ijimai. 

 The other species are larger, and have a large number of tentacles, 

 from 18 to 24 pairs, and appear therefore to be related to P. 

 australis and P. buskii. A figure of this type of larva is given 

 from a specimen from Ceylon, for the loan of which I have to 

 thank Professor Goodrich. 



A. spauldingi, Cahfornia, measuring 1-75 mm., eleven pans 

 tentacles, is believed with reason to be the larva of P. pacifica, 

 and it is evidently related to the Japanese A. ikedae. 



As a result of this rough and somewhat cursory analysis I 

 venture to suggest that we have m the North Atlantic and Mediter- 

 ranean what may be called two specific types : — 



Phoronis ovalis with Actinotrocha branchiata. 

 P. hippocrepia with A. pallida. 



In the Indo-Pacific region, in addition to species alhed to if 

 not identical with P. hippocrepia, there are large species of the t}^De 

 P. buskii which are pecuhar to the East Indian region, and these 

 too are related to P. hippocrepia. The northern Atlantic forms 

 may thus be imagined to have gained the north as far back as 

 the late Mesozoic when the Indian Ocean was formed and the way 

 opened to spread into European waters. 



The planktonic period may be longer than has been beheved, 

 and it is not unlikely that it may be prolonged under certain 

 conditions. Willey, for example, was perhaps not so far wrong 

 when he identified the specimen he got in New Brunswick waters 



