. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 500 Btilletin Museum of Comparative Zoology, Vol. 144, No. 8 ethmoid frontal sphenotic parietal supraoccipital. epiotic exoccipital orbitosphenoid pterosphenoid parasphenoid basioccipital 1 mm intercalar Figure 9. Landonia latidens. Lateral view of cranium ( specimen). for the dentary are entirely enclosed within these bones (Figs. 6, 15). In the mnlticnspid teeth of Fhenacohnj- con and Landonia each cusp represents a separately formed conical element. In the fomiation of the peculiar straight-edged teeth of La
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 500 Btilletin Museum of Comparative Zoology, Vol. 144, No. 8 ethmoid frontal sphenotic parietal supraoccipital. epiotic exoccipital orbitosphenoid pterosphenoid parasphenoid basioccipital 1 mm intercalar Figure 9. Landonia latidens. Lateral view of cranium ( specimen). for the dentary are entirely enclosed within these bones (Figs. 6, 15). In the mnlticnspid teeth of Fhenacohnj- con and Landonia each cusp represents a separately formed conical element. In the fomiation of the peculiar straight-edged teeth of Landonia, however, there is no sign of separate conical elements, at least not in alizarin preparations, \^^len these teeth first show signs of ossification the\- have already acquired a perfecdy straight- edged crown. After examining five alizarin prepara- tions of Landonia, I am inclined to think that all of the teeth on both sides of its jaws are replaced in one continuous and relatively rapid ("simultaneous") act. The reasons are: 1) in none of the specimens does there appear to be differential wear of the teeth on one side of the jaws, nor do the teeth on one side of tlie jaws differ in any odier way (such as coloration, density of alizarin uptake) from those on the other side, as one would expect to find in a characid with replacement alternating from side to side; 2) in four of the five specimens the replacement teeth (note: the replacement teeth enclosed in their re- spective bones are visible through the bone, and the replacement teeth for the internal row on the premaxillary lie ex- posed in the gum) on both sides of the jaw are in the same stage of formation; and 3) in the remaining specimen, mm, there are no ossified replacement teeth on either side of the jaws and the functional teeth appear unworn and newly arrived in position. Finallv, in a population sample of 24 Landonia (MCZ 48664), there are 23 specimens in which all of the teeth on both sides of
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