370 Davis — On the Fossil Fish of the Cretaceous Formations of Scandinavia. 



Oxyrliina, he observes that iu the young stages of Lamna the teeth are without 

 lateral denticles, and that these onl}^ develope later. Of the genus Otodus, he 

 remarks that it is closely allied with Lamna, from which it only differs in the 

 greater development of the lateral denticles, their broader and less slender form. 

 The teeth of Otodus, whilst having the form of those of Carcharodon, are not 

 serrated on the margins, but in the opinion of M. Sauvage the three genera 

 named are closely related. He quotes an observation of M. Pictet, that these 

 teeth in many instances vary more from different parts of the same mouth than 

 their homologues in another sjjecies, and that this variation renders the difficulty 

 of the interpretation of their exact specific characters very great. This observa- 

 tion applies with considerable force to the genera Lamna and Odontaspis, the 

 teeth of which closely resemble each other ; but the fishes still existing enable the 

 naturalist to study and compare them, and their relationship is far more distant 

 than some of the other genera whose teeth have less resemblance. Palseonto- 

 logically it is very difficult to separate tlie two genera, which are quite distinct in 

 living examples. 



In the year ISoi Valerian Kiprijanoff described a number of Selachian teeth 

 from the Cenomanian ferruginous sandstones of the governments of Kursk and 

 Orel, in Russia.* The characteristics of the teeth of the genera before named, 

 as defined by Agassiz, are cited ; [the difficulty of determining fragmentary 

 examples is stated to be almost insurmountable, and the microscopical examination 

 of the structure of the crown of Otodus, Lamna, and Oxyrhina is found to afford 

 no definite characteristics. The description of several species of Otodus, led the 

 author to seek the relationship of the genus with other associated forms, and he 

 expressed the opinion founded on his investigation, that the broad teeth approach 

 most nearly to Carcharodon, whilst towards the opposite extreme their similarity 

 to the teeth of Lamna stand out clearly. Specimens witliout lateral denticles are 

 indistinguishable from the teeth of Oxyrhina. Kiprijanoff states that in young 

 examples the teeth of Odontaspis possess lateral denticles at an earlier stage than 

 do those of Lamna ; and he regrets that an example of the jaw of Otodus has not 

 been found, so that some information as to the arrangement of the teeth in situ 

 might be obtained. 



Professor Zittelf accepts the general definition of the genera of the Lamnidse, 

 and cites the opinion of C. Hassfe % tbat the Lamnidse have developed from the 

 Scylliolamnidse, with which they are nearly connected, especially through the 



* Fisch-TJeberreste im Kurskschen eisenlialtigen Sandsteine by Valerian Kiprijanoff ; Bull, de la Soc. 

 Imperiale des Naturalistes de Moscou, 1854, vol. xxvii., p. 373. 



f Handbuch der Palfeontologie von Karl A. Zittel, band iii., p. 81. 1887. 



\ Das NatiirUche system der Elasmobranchier von C. Hasse ; 1879 : see Stammtafcl i. 



