Notes on the Stenomorphic Form of the Shipworm 83 
waters south of Cape Cod. The laths of which the 
lobster pots are made are often completely riddled in a 
few weeks. The number of stenomorphic specimens in 
these laths is no greater proportionately than one finds 
in heavy piling and the average size of a larger number 
of specimens removed from the laths is the same as 
that of specimens removed from big timber. ‘Also, large 
blocks, made up of many shingles bolted more or less 
tightly together (Mark, 1924, p. 266, footnote 3, p. 268, 
fig. EZ), were placed at fifty or more stations from Massa- 
chusetts to Texas. In some of these shingle blocks, 
stenomorphic specimens occurred, but in the majority 
the specimens were not stenomorphic, but nearly or en- 
tirely normal. Because of the fact that the average 
shipworm will endeavor to avoid crossing a large crack 
or open area in the wood, as long as progress is possible 
in some other direction, many of the shipworms in the 
shingle blocks made more or less of an effort to remain 
within a single shingle, the effort depending entirely 
upon how firmly the shingles were bolted together. 
When the specimens entered the thicker end of the 
shingle and advanced with the grain of the wood toward 
the thinner end, this effort to refrain from crossing to 
the adjacent shingle, resulted in a peculiarly abnormal 
form, in which the tubes are excessively attenuate. 
Many of these specimens were found which had attained 
a tube length of 400 millimeters in three months, but, 
owing to the thinness of the wood, had increased the 
diameter of the tube very slowly. The anterior ends of 
many of these long tubes were frequently but five milli- 
meters and occasionally only four millimeters in 
diameter. The shipworm is able to contract its body 
into one-half of its normal length. The body is firmly 
attached to the wall of the burrow only at the extreme 
