FOSSIL GENUS BASILOSAURUS. 11 



I have two fragments of this maxilla — one five inches loner containing^ a canine 

 tooth with the alveoli of two others, (PI. Ill, figs. 5 and 6,) and the other of the 

 opposite side, about three inches. The characters of these specimens I thought were 

 more Saurian than Cetacean ; there being distinct pits on the outer surface of the jaw, 

 showing the overlapping of the upper teeth as in Saurians ; and the vertebrae having 

 a strong tendency to become convex posteriorly. However, I am now satisfied that 

 they belong to Z. cetoides. 



Among the fossils of the Eocene period found with these relics, are tympanic bones 

 and teeth of cetacca resembling Physeter macrocephalus, and Baicena ajjinis, Owen, 

 as given in his " British Fossil Mammalia." Several vertebrae of a Delphirius, teeth 

 of a true crocodile, and others with a compressed lateral cutting edge similar to figures 

 given by Prof Owen in his Odontography, as of extinct Saurians, which Prof. Agassiz 

 informs me have been figured by H. Von Meyer, under the name of Madrimosaurus; 

 a fossil that appears to me to have an analogue in the Crocodilus macrorhyncus of 

 Harlan.* 



Here also I found teeth of a large Pristis, (PI. I., fig, 6 and 7,) differing from 

 P. acutidens, Agassiz.f The prevalence of Cetacea and Sauria at this period, 

 together with that of fossils common to the cretaceous and Eocene beds, are inte- 

 resting facts. These Eocene beds are the lowest in ihe series, and contain Gryphcea 

 miitahilis, (Morton,) and Terehratula Harlani, (Morton,) which are also found in the 

 cretaceous formation ; while Cardita planicosla, (Sowerby,) Scutella Lyelli, (Conrad,) 

 Pecf.en membranosus, (Morton,) and other fossils, characterize them as Eocene. 



When the Maestricfit monitaur was discovered, it was a long time before naturalists 

 were able to decide its position in the scale of organized beings. Camper and Van 

 Marum considered it Cetacean; Hoffman, Drouin, and Faujas de St. Fond insisted 

 that it was a Crocodile ; but Adrien Camper decided it was neither cetacean, fish, 

 nor crocodile, and referred it to a new genus of Sauria related to the Monitor, and to 

 which Coneybeare gave the name of Mosasaurus. Subsequently Cuvier confirmed 

 the opinion of Camper.f Since that period various new genera have been added to 

 this remarkable class of fossil reptiles, yet doubts have existed whether some of them 

 do not possess affinities to the Mammalia. Cuvier has laid down the following rule, 

 which is now generally admitted : 



" En Zoologie, quand la tete, et surtout les dents et les machoires, sont donnees, 



* Medical and Physical Reiearches, p. 380; and Journal of Academy of Natural Science, Vol. IV., p. 15, 1824. 



t This Pris/is' bears some resemblance to P. acutidcm. Agassh, bat differs in tapering more gradually from the 

 root to the point which is more acute. The root is thicker and longer in proportion, and the groove or channel 

 on the posterior edge is deeper, and extends to the point of the tooih. The body is rather more pyramidal than 

 conical, as in P. acutidens. I propose for it the name of Pristis agassizi as a small tribute to the distinguished 

 author of the great work " Sur les Poissons Fossiles." 



X Cuvier, O.ssemens Fossiles, Tome V., p. 314. 



