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 ])osterior 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 jNIyliobatidae. 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 toath, 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 apai't 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 af)pear, 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 

 amons 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 multij^lication of synonyms for both 



