Ko. 639] 



AMERICAN FOLLICULINAS 



365 



in fact, the tube and sac grade into one another and stand 

 straight up from the attachment. This is by means of a 

 long cylinder of cementing material, bringing the base of 

 the animal well above the substratum. There may be a 

 simple membraneous valve. 



Of the two species, P. mellita was taken in the Antarc- 

 tic in 1902-3 by Laachmann at depths of 350-385 meters 

 and its case has a length .6-7 mm., but this great length 

 is partly due to the mode of attachment of the sac by 

 means of a stalk of secretion. As this stalk is hollow and 

 filled by a tenuous prolongation of the body of the animal, 

 it may be that this genus also is founded upon individual 

 idiosyncrasies of secretional activity. 



The other species, P. arctica, has been formed by Dons 

 to include the smaller but similar forms he found in Nor- 

 w^ay and finally separated from P. mellita as smaller, 

 with narrower stalk apparently not perforated. 



As the above eleven species have been most studied in 

 England, Germany and Norway, it is natural that Folli- 

 culinas are known chiefly from those coasts; yet the 

 known distribution of Folliculinas has already been ex- 

 tended to the Antarctic, the Mediterranean, the White 

 Sea, as well as to the oast and west coasts of the North 

 Atlantic. On the east coast of the United States we seem 

 to have four or five species in two of Dons's subdivisions 

 of the old genus FoUiculina, namely : the most specialized 

 and best knowTi Semifolliculina producta of the shores of 

 the Chesapeake; the accompanying small and simpler 

 form Parafolliculina amphora; the less well-marked form 

 Semifolliculina boecki, first found at Newport, R. I., and 

 later at Woods Hole, Mass. ; and finally, as recorded by 

 Dons, from material from the North American Atlantic 

 coast the Semifolliculina spirorhis; and if Dons's Para- 

 folliculina violacea be a real species, it also is to be cred- 

 ited to Woods Hole. 



That some or all of tlio smaller and simpler forms arise 

 from larger and more coinplcx loinis under changing 

 conditions of nutrition in llu' siu-ccssivo phases of seden- 

 tary and free life is a tempting working hypothesis. 



