THE MORPHOLOGY OF THE HINGE TEETH OF 
BIVALVES. 
WILLIAM H. DALL. 
Tug most notable step in advance for the study of bivalve 
mollusks which has been made for many years is due to the 
researches of the late F. Bernard, which are included in half a. 
dozen papers, of which the earliest appeared in 1895. 
Ever since the time of Schumacher and Lamarck, in the 
early years of the century, the interlocking projections of the 
dorsal margins of the valves of pelecypods have been recog- 
nized, under the name of hinge teeth, as affording characters 
of the highest value in systematic classification of the subdi- 
visions of this group. All works treating of these animals 
have utilized the more or less obvious features of the adult 
hinge teeth in framing diagnoses of families and genera. 
Systematists contented themselves, however, with noting the 
number, position, and division of the teeth into so-called “ car- 
dinals” and “laterals ” and ignored the fact that large groups 
have teeth of special types, which can hardly be closely homol- 
ogized with the teeth characteristic of several other groups. 
This method of treating the teeth was unquestioned for more 
than, half a century and became so fixed in the minds of sys- 
tematists that modern efforts to suggest a new point of view 
have up to the present time been almost futile. Steinmann, in 
his Lehrbuch der Paleontologie, Fischer, in his Manual (1887), 
and especially Neumayr, in his Morphologie Bivalven Schlosses 
(1883), emphasized the necessity of distinguishing between 
certain fundamental classes or types of hinge teeth, and to 
Steinmann we owe the suggestion of a formula for indicating 
in brief form and almost graphic manner the number and rela- 
tions of the teeth on any given hinge. The writer, in 1889, and 
Neumayr, in a posthumous paper issued in 1891, applied these 
principles to the general classification of bivalves, necessarily 
175 
