NOTES ON THE STENOMORPHIC FORM OF 
THE SHIPWORM. 
W. F. Crapp. 
The term stenomorph has been given by Dr. Bartsch 
(Bartsch, 1923, p. 330) to those specimens of shipworms 
which are abnormal in being dwarfed, although they may 
be sexually mature. Dr. Bartsch discovered the fact 
that this form is frequently found in small pieces of wood 
and inferred that it is caused by the cramped habitat 
of the individual. A study of the stenomorphic specimens 
found in the test-blocks placed by the Committee on 
Marine Piling Investigations of the National Research 
Council (Clapp, 1923, p. 31) has added further evidence 
of the conditions which cause this peculiar form. 
The shell of the stenomorphic specimen (pl. 4, fig. 1) 
may generally be distinguished from the normal speci- 
men of the same species by its smaller size and greater 
shell thickness, as well as by the proportionately greater 
number of denticulate ridges on both the anterior and 
the anterior-median areas of the shell. The internal 
blade or apophysis is greatly broadened and strength- 
ened (pl. 4, fig. 2). There is, however, no sharp 
dividing line between the stenomorph and the normal 
Specimen of the same species. Many large specimens, 
with tubes 250 millimeters or more in length, show 
traces of stenomorph characters in those portions of 
the shell last secreted. There is a well-graded series 
between these large, nearly normal specimens and those 
typical stenomorphs of the same age which possess tubes 
only ten millimeters long. In the typical stenomorph 
the auricle is entirely lost, being overlaid by the an- 
