54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ^2 



expect a departure from the typical dentition — more teeth. Of the 

 cheekteeth there are only known a few that are tolerably complete; 

 that every one of them had seven marginal cusps is mere conjecture 

 and not probable ; in other cetacea with serrate teeth, both Zeuglo- 

 donts and Squalodonts, the number of cusps varies strongly; no 

 cetacean is known in which the same number of cusps is found on all 

 the cheekteeth. Some dissociated teeth that probably are correctly 

 referred to Pafriocetus (Sqnalodon ehrlichii), figured by Suess 

 ( Neue Reste von Squalodon aus Linz ; Jahrb. d. k. k. geol. Reich- 

 sanstalt, vol. i8, 1868, pp. 287-290, pi. 10, figs. 1-3) and reproduced 

 by Brandt (Unters. foss. u. subfoss. Cetaceen Europa's ; Mem. Acad. 

 Imp. Sci. St. Petersbourg, ser. 7, vol. 20, No. i, 1873, P^- 3i> %s. 

 11-13), also show other numbers, one of them 9, another 10. More- 

 over it is doubtful whether Patriocctus can be regarded as an ancestor 

 of the whalebone whales ; it is not precluded that with more exact 

 acquaintance it will show itself to stand on a higher level, nearer to 

 the typical Squalodonts, closely connected with Agorophius (see 

 note. p. 72). In short the whole calculation about the 53 teeth in the 

 whalebone whales and the 53-tooth cusps in Patriocetus rests on the 

 weakest foundation. 



It is also a question whether Kiikenthal and Abel are on the whole 

 right in their conception of the many small teeth of the whalebone 

 whales as having originated by the division of fewer, larger, serrate 

 teeth. There is indeed scarcely any doubt that a division of the tooth 

 germ might be able to take place at an early stage of a tooth's develop- 

 ment; but that a tooth which had already acquired serrate margins 

 should be able to divide is not probable ; in the case of the whalebone 

 whales at any rate there is nothing convincing in this respect — quite 

 the contrary ; and other cases are not known. The " double-teeth " 

 of the embryo whalebone whales are the ones that are conceived to 

 be serrate teeth in course of division; but they could be better ex- 

 plained in another manner. Their position in the toothrow is quite 

 erratic — sometimes far to the front, sometimes in the middle or far 

 back. The number of cusps is most often two, only in rare instances 

 as many as four. The cusps have the appearance of being of equal 

 rank, none can be called the chief cusp. In short, the cusps in the 

 double teeth appear to be small, atrophied, unicuspid teeth which 

 have quite casually come near each other and grown together, some- 

 thing which might be able to take place with special ease in the 

 youngest stages of the embryo when the tooth germs are crowded 

 together in relatively short jaws. That double teeth were produced 



