104 THURLOW C. NELSON. 



intensity of ship-worm infestation and of oyster sets. In 1921 and 

 in 1922 heavy sets of Ostrea, Teredo, and Bankia occurred. The 

 oyster set in 1921, especially, was the heaviest seen for some 

 years, as high as 1000 oyster spat attaching to one oyster shell 

 (Xelson, '23 A). The sudden and heavy outbreak of Teredo 

 navalis at the same time (Nelson, '22) gave rise to fears that 

 there might be enacted in eastern waters a repetition of the San 

 Francisco Bay disaster (Kofoid et al., '21). It will be noted in 

 Table I. that Mnemiopsis was absent or rare in Barnegat Bay and 

 adjoining waters during 1921 and 1922. 



The oyster set in Barnegat Bay in 1923 was a failure com- 

 mercially. The best set that could be found at the close of the 

 summer was one or two spat on every third oyster shell. The 

 total season's catch on certain experimental shells was only 7 spat 

 as against over 7000 in 1921. 



Teredo navalis infested timbers in numbers as great as 100 per 

 cubic inch of wood in 1921, while in 1923 at the same spot only 10 

 Bankia entered a test raft of 1,520 square inches surface. This 

 very light infestation occurred in spite of the prevalence of 

 slightly higher salinities obtaining in the region than were found 

 in 1921. At only one locality, the jetty at the mouth of Barnegat 

 Creek at the lower end of the Bay, could enough Teredo be 

 found even for carrying on experiments with them. This jetty 

 has been heavily attacked by borers for some years and w r as 

 practically destroyed in 1921. Two infested piling were removed 

 from this structure on July 25 and 5 were taken August 31, 1923. 

 They were moored in a small land-locked creek close to the upper 

 end of the bay, far from marine structures, and were used as a 

 source of supply for study of the heterotrichous ciliate Boveria 

 teredinidi Nelson, parasitic upon the gill filaments (Nelson, 

 '2T)B). Throughout the summer and autumn until freezing 

 occurred the borers grew and flourished, thus proving that no 

 natural conditions present in the bay during this period were 

 inimical to the existence of the adults. 



The Director of the Committee on Marine Piling Investigations 

 of the National Research Council, Col. Win. G. Atwood, informed 

 me in a letter of October 23, 1923, that "on the whole shipworm 

 attack on test blocks was much lighter during 1923 than in 1922, 

 although at one or two points it appears to have been as heavy 



