MARYLAXD GEOLOGICAL SURVEY 83 



They are extremely rare in the Maryland Eocene, and are not at all 

 common in the Miocene. The lateral tooth from Fairhaven, shown in 

 Plate XXXI, Fig. 3, is one of the largest found in this state, although 

 it is exceeded in size by some of the same species from South Carolina, 

 California and Peru. Those from Plum Point are mostly of small size, 

 comparatively speaking, and have thinner and flatter crowns, as shown 

 in Plate XXXI, Fig. 2. These agree with the teeth described by Agas- 

 siz as a distinct species under the name of C. produdus, but now re- 

 garded as a variety of the present form. " Carcharodon angustidens " 

 (= C. auricidatus Agassiz) is recorded from Charles county by Cope, 

 but no examples exist in the collection. 



Occurrence. — Calvert Formation. Charles county near the Patux- 

 ent river. Plum Point, Fairhaven. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 Philadelphia Academy of Xatural Sciences. 



Family CARCHARIIDAE Miiller and Henle. 



It is a noteworthy fact that the gradual decline of the Lamxidae 

 during Tertiary time was accompanied by a remarkable increase in im- 

 portance of the genera included under the Carchakiidae, and evidence 

 is not lacking to show the latter have been able to displacfe the Lam- 

 NiDAE by means of their more efficient organization. Although their 

 dentition does not appear formidable in comparison with the gigantic 

 teeth of Carcharodon, it is in reality more durable, making up in struc- 

 ture what it lacks in size. In the teeth of this family the nutrient 

 canals are concentrated into a central pulp-cavity, and the greater part 

 of the crown consists of vasodentine. Xot only is there much variation 

 among the teeth of the upper and lower jaws, but it often happens that 

 teeth of the upper jaw in one species have the same form as those of 

 the lower jaw in a different species, thus rendering the determination 

 of isolated fossil teeth very imcertain.' 



iBei den Carcbariden erschwert jeue Verschiedeuheit der Ziihiie in Ober- und 

 Unterkiefer die speciflsche Bestimmung einzelner Ziihne uugemein, weil hiiuflg die 

 Zahnformen des einen Kiefers einer Art im entgegengesetzten Kiefer einer nahe ver- 

 wandten Art wiederkebren. Man muss sicb iufolge dessen zunacbst immer klar zu 



