256 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
less of a prominence, due to the median series of tritors, on the hinder margin. 
The tritors with some irregularity are distributed in four rows: an outer series 
at the edge of the tooth of about six rounded tritors, an inner series of about 
three near the front end, a median series of several parallel with the inner, 
and a posterior series of about nine broad, short, closely placed tritors extend- 
ing from the hind margin forward over more than half of the tooth and to 
some extent resembling the dental series of certain Myliobatidae. The mandi- 
bulars are pointed at each end and convexly curved on both outer and inner 
margins; they bear an outer series of small rounded tritors anteriorly, along 
about two-thirds of the edge of the tooth, and a median or posterior series of 
broad, short, closely packed tritors in the hinder three-fifths of the tooth, ex- 
tending to the hind margin, but not to the posterior extremity. The descrip- 
tion immediately foregoing is taken from a specimen that had almost reached 
maturity, and may be said to fairly represent conditions in an adult, Plate 5, 
Figures 3 and 4. The appearance of the teeth in a half-grown specimen are 
indicated on Plate 5, Figures 6 and 7. Of such immature specimens the teeth 
are farther apart and on each tooth the angles are less developed. The tritors 
also are farther apart and much smaller, some of the hindmost of the wide 
ones of the inner series being very faintly indicated or altogether absent. 
Each of the teeth at this stage may be described as shorter, broader, and less 
angular than the corresponding tooth of the adult. In quite young specimens, 
such as that of which the teeth are figured on the same plate, Figures 8 and 9, 
the teeth are less broad and more angular and tritors have not appeared. This 
in all likelihood represents the condition obtaining in the adult of some ances- 
tor; and this stage is nearer to the permanent type in Rhinochimaera. While 
there are no tritors on these teeth the positions they finally occupy are already 
indicated by slight ridges or swellings. A still earlier stage would probably 
bear teeth on which these ridges would not be developed. 
The teeth of very young Callorhynchidae, Plate 6, Figures 3 and 4, before 
the tritors appear, are similar to those of a like stage in the Rhinochi- 
maeridae, as represented by Harriotta, Plate 5, Figures 8 and 9. In later 
stages the tritors appear on the ridges of palatines and mandibulars and on 
the cutting edges of the vomerines. This condition appears to be retained 
by the adult in the type here identified with Callorhynchus smythii Benn., of 
which the teeth are shown on Plate 6, Figures 1 and 2. In the other species 
of the genus, however, the hinder portions of the tritors of the palatine teeth 
enlarge and fuse, while the forward portions remain as two prongs that may 
apparently become less extensive toward the front; at the same time the tritor 
of each mandibular tooth shortens and broadens until in cases somewhat angu- 
lar or nearly round, as in Callorhynchus milii, Plate 7, Figures 7 and 8. If in 
addition to the individual variations those shown to occur in the five species of 
this genus at hand are also considered, we get a hint of what may be expected 
among other genera, recent or extinct. Teeth from the various stages of indi- 
viduals, or of the different species detached and described, as is necessarily 
done with fossils, might readily lead to multiplication of synonyms for both 
