MARYLAND GEOLOGICAL SURVEY 33 



and a narrower one on the outside. The tooth is marked by numerous 

 irregular transverse lines, similar to those frequently marking growth, 

 and by longitudinal shallow grooves. The pulp-cavity extends for two- 

 thirds the length of the tooth, being thus relatively deeper than in the 

 known species, and is also very large, thinning the external wall out 

 to an open basis. In the known species the walls are relatively thicker, 

 and for a considerable distance parallel to each other. The form of 

 the tooth is in some degree similar to the crown of the canines of some 

 crocodiles. There is no enamel on the teeth of Cetaceans of this genus. 



"Total length, 2 inches, 5 lines; long diameter at base, 8.35 lines; 

 diameter at middle, 6 lines." Cope, 1867. 



In 1869 Leidy repeats the characters of 0. cornutidens: "conical, 

 strongly curved, and. proportionately much broader approaching the 

 base than in the preceding species [0. quadratidens] ; nor does it assume 

 a quadrate appearance, but is nearly circular or ovoidal in transverse 

 section. The deep conical pulp cavity is defined by a sharp edge at the 

 periphery of the base." 



In this article Leidy remarks that Cope's 0. crocodilinus is most 

 likely a young individual of 0. cornutidens, also he says that in the 

 light of the great variability in the teeth of the Physeteridae in 

 general that he regards it as very possible that all three species, de- 

 scribed from teeth, belong to the same species. 



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

 ent river. 



Collection. — Cope's type of 0. crocodilinus is in the Museum of the 

 Academy of Natural Sciences of Philadelphia. 



Suborder MYSTICOCETI. 



In this suborder the teeth are never developed beyond an embryonic 

 condition. Eudimentary teeth which disappear before birth are inter- 

 esting indications of the ancestry of the forms. The upper jaws are 

 greatly arched and from their lower sides depend the great plates of 

 baleen, "whale-bone," which give to the animal its characteristic ap- 

 pearance; the lower jaws are greatly arched in a horizontal plane. The 

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