102 SYSTEMATIC PALEOXTOLOGY 



Aetobatis AECUATrs Agassiz. 

 Plate XIII, Figs. 3a, 3b, 8. 



Aetobatis amtatus Agassiz, 1843. Poiss. Foss., vol. iii, p. 327. 



Aetobatis arcuatus Cope, 1867. Proc. Acad. Nat. Sci. Pbila., p. 139. 



Aetobatis profundus Cope, 1867. Loc. cit., p. 139. 



Aetobatis arcuatus Leidy, 1877. Jour. Acad. Nal. Sci. Pliila., 2nd ser., vol. viii, p. 



24.5, pi. xxxi, figs. 14-18. 

 Aetobatis profundus Leidy, 1877. Loc. cit., p. 246, pi. xxxi, tigs. 19, 20. 



Description. — This species is known only by fragments belonging 

 chiefly to the lower dentition, and consequently cannot be accurately 

 defined. Founded originally on detached teeth from the Miocene of 

 Switzerland, it has been recognized by Cope and Leidy from the corre- 

 sponding horizon in Maryland, but has not been hitherto reported from 

 the Eocene. It would appear to be very rare in the latter formation, 

 as only a few detached teeth have been collected by the Maryland Geo- 

 logical Survey. A number of Miocene forms from Charles county are 

 figured by Leidy {loc. cit., 1877, pi. xxxi), Avho very plausibly suggests 

 that the narrow rounded crowns described by Cope as A. profundus are 

 in reality only worn anterior teeth belonging to the species under con- 

 sideration. Other species of Aetodatis occur in the Eocene of New Jer- 

 sey and South Carolina. 



Occurrence. — Nanjemoy Fokmation, Popes Creek. Aquia Foema- 

 TiON. Aquia Creek. 



Collection. — Maryland Geological Survey. 



Suborder ASTEROSPONDYLI. 

 Family CESTRACIONTIDAE. 



Genus SYNECHODUS Woodward. 



This genus of Cestraciont sharks is known by the nearly complete 

 dentition and parts of the skeleton in the Lias of England, where it 

 accompanies such allied forms as Tlybodus, Acrodus, etc., and detached 

 teeth have also been described from the Cretaceo-Tertiary of New Zea- 

 land. Its remains have not been heretofore reported, however, from 

 strata of undoubted Tertiary age, and the following species may be re- 

 garded as the latest survivor of the genus of which we have any record. 



