342 Jordan — Sharks' Teeth from California. 



those at the base and tip. Tip of the tooth sharper than 

 in any of the others, the root less concave in outline, the 

 crown narrower, its base l 1 /^ in its height. 



4. Isukus planus (Agassiz). 



(Oxyrhina tumulus Agassiz: Isurus smithi Jordan). 



From the same deposit, I have the tooth of an Isurus, 

 the crown of which is 1% inches high, the tooth narrow 

 and nearly erect, corresponding fairly to the figures of 

 Isurus smithi Jordan (p. 11), but broader at the base than 

 any of those figured, the base of the crown being two- 

 thirds its height. 



As in this genus, the teeth are very differently formed 

 in different parts of the mouth. I do not lay stress on 

 these differences, and I have no doubt of the identity 

 of Isurus planus, tumulus and smithi, all from the 

 Kern County beds. And these differ but slightly from 

 Isurus hast alls (Agassiz) of Europe, with which Jordan 

 and Beal, in a later paper (op. cit., vol. VII, 251, 1913), 

 following Maurice Leriche, have identified them. In 

 most of the specimens figured by Agassiz, however, as 

 has talis, the inner face of the tooth has an obsolete ridge. 

 This appears on one or two only of our multitude of speci- 

 mens of Isurus planus. In view of the fact that all these 

 California fossils have been described as distinct species, 

 it is better to retain these names until adequate com- 

 parison can be made with related species in European 

 deposits. The living sharks along the Pacific Coast have 

 yet to be critically compared with their Atlantic relatives, 

 and in most cases where comparison has been made, the 

 species are found to be distinct. 



From Torrance, I have also three much smaller teeth 

 which may be merely the young of the same species as 

 they seem too large for the living Mackerel Shark, Isurus 

 glaucus (Miiller & Henle), still extant in the Pacific. 

 These come from different parts of the mouth, one, a slen- 

 der median tooth, being an inch high. 



The genus Isuropsis Gill, represented in both oceans, 

 has the teeth essentially as in Isurus proper {Oxyrhina 

 Agassiz) but the lateral teeth are more slender. Isurop- 

 sis is probably not tenable as a distinct genus. 



Stanford University, California. 



