39 



the larva is liable. The youngest larva I saw at St, Andrews had 

 six pairs of tentacles, and had therefore been free for some time. 

 The majority found in St. Andrews Bay are already advanced 

 in growth, and young Phoronis are found almost as soon as the 

 larvae. It is not the same stock that is found throughout the 

 three or four months of the summer and autumn, but a stock 

 which is being constantly supplied by the currents, in this case 

 from the north. The species like other meroplanktonic forms 

 may be pictured as being rotated generation after generation 

 along with the prevaihng current of the region. It may be pelagic 

 for many weeks, and thus have the time to be carried a long distance 

 before it reaches the bottom, and there is no contranatation. With 

 this in mind an attempt may now be made to briefly consider the 

 described species of Phoronis and of Actinotrocha. 



2.— SPECIES OF PHORONIS. 



PJwronis ovalis, Strethill Wright. — The characters and the 

 distribution have already been given. The Phoronis described 

 in 1858 by van Beneden * under the name Crepina gracilis may be 

 included here. It was obtained in an oyster shell, but van Beneden 

 did not state where the shell was procured. The lophophore 

 was similar to that of P. ovalis. The animal had a length of 8-10 

 mm., and a diameter of about 1 mm. The tentacles were found 

 to be very variable in number. " Nous en avons compte quelque- 

 fois vingt-quatre, d'autres fois le nombre s'elevait a trente et meme 

 quarante." Van Beneden observed also the renewal of the 

 tentacular crown. De Selys Longchamps f has described P. 

 mulleri from Hehgoland, and beheves that it is derived from A. 

 branchiata. If this be the fact and the above contentions sustained, 

 then the size is still further increased — to 40 to 80 mm., and the 

 number of the tentacles to 50 to 60 ; the longitudinal muscles 

 number 24. De Selys Longchamps states that the left lateral 

 mesentery is not developed. This is evidently also the case in 

 P. ovalis as it is in the metamorphosed Actinotrocha hranchiata. 



Phoronis euxinicola, de Selys Longchamps, got at Sebastopol, 

 is nearly alhed. The lophophore has, however, the shape " 5," 



* Ann. d. Sc. Nat. (Zool.), T. 10, p. 11. 



t Wiss. Meeresunters Kiel u, Helgoland, Bd. VI., 1903. 



