82 Trans, Acad. Sci. of St. Louis 
terior-median area, since the denticulate ridges of this 
area completely cover the entire median area and also 
the auricle to its posterior edge. The anterior area 
is also proportionately large, the denticulate ridges of 
that area being added to its ventral edge until it is 
nearly as large as the anterior-median area both in 
length and in height. In a young normal specimen of 
Teredo navalis, the ridges of the anterior area are 
approximately one-fourth the width of the intervening 
spaces (pl, 4, fig. 3). In a typical stenomorphic speci- 
men of the same species and of the same size, the den- 
ticulate ridges of the anterior area are so closely 
crowded that the spaces between the ridges are reduced 
to mere threads (pl. 4, fig. 4). This dwarfed form, while 
the same age as a large normal individual, may be but 
one-tenth of its size. The embryos in the gills of a 
sexually mature stenomorphic specimen are much less 
numerous than are the embryos in a normal specimen 
of the same species, but in all other respects the embryos 
are identical. 
At many of the places where test-blocks have been 
placed by the Committee on Marine Piling Investiga- 
tions, these stenomorphic specimens are frequently 
found in the wood, and since the blocks used in 1922 
were small (2 inches by 4 inches), it was thought that 
the abnormality was caused by the cramped quarters. 
As Dr. Bartsch states (loc. cit.), they are frequently 
found in laths and other small pieces of wood, but that 
some factor other than the size of the wood enters into 
the result, is shown by the fact that laths and small 
pieces of wood frequently contain large and perfectly 
normal specimens. For example, Teredo navalis causes 
considerable damage to the wooden lobster pots in the 
