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A NEW FOSSIL PORPOISE FROM MARYLAND. 



In the foregoing table are given the dimensions of the type and other teeth 

 of D. leidyi in The Academy of Natural Sciences of Philadelphia and of the two 

 detached teeth from Chesapeake Beach above mentioned. 



The average diameter of these six teeth at the base of the crown is 7.6 mm., 

 while the average for 42 teeth from the Chesapeake Beach skeleton is 5.2 mm. 

 The average maximum diameter of the root in the six teeth of D. leidyi is 6.8 mm. 

 and in 38 teeth from the Chesapeake Beach skeleton, 5.3 mm. This marked 

 difference in the size of the teeth can hardly be regarded as due to the difference 

 in age which is observable, or to individual variation. The roots might, and 

 probably would, increase in diameter with age, owing to the deposit of cement, 

 but the same cannot be said of the crowns. The conclusion seems inevitable, 

 therefore, that the Chesapeake Beach skeleton represents a species allied to 

 Delphinodon leidyi, but having smaller teeth. If this be correct, it would, of 

 course, be expected that D. leidyi, when better known, would be found to possess 

 various osteological characters which would render it distinguishable from the 



Chesapeake Beach species herein described 



It seems best, under the existing 



circumstances, to regard the latter as a separate species, and a diagnosis of it 

 and of the genus Delphinodon, to which it is supposed to belong, are appended. 



Genus DELPHINODON Leidy. (Emended.) 



Skull broad and depressed. Rostrum short, triangular. Premaxillae broad 

 and flat on the sides and in front of the nares and extending backward to the 

 sides of the nasals. Nasals oblong, directed forward. Free margin of the orbital 

 plate of the maxillae thin. Symphysis of the mandible long. 



Posterior teeth with distinct accessory cusps, and crowns of all the teeth with 

 rugose enamel, and anterior and posterior longitudinal ridges, the former more 



or less bifurcated at the base. 



Cervical vertebrae all separate. The atlas with a single transverse process 

 on each side, a complete foramen for the exit of the first spinal nerve, and an 

 inferior median facet for articulation with the odontoid process of the axis. 

 Third to sixth cervicals with the vertebrarterial foramen completed surrounded 

 by bone. Spines of thoracic vertebrae erect. Lumbars moderately elongated 



> 



More than 



their transverse processes narrow, and tapering at the extremity, 

 eleven pairs of ribs; the anterior pairs with both head and tubercle. 



Humerus elongated, with a distinct pit on the outer side of the shaft, -tta l 

 strongly curved. Ulna with a large, lunate olecranon. 



Delphinodon dividum new species. 



Size small. Rostrum of the skull a little more than one-half the total length. 

 Symphysis of the mandible about one-third the total length of the latter. r - 

 maxillae opposite the nares about as wide as the portion of the orbital pa 



the maxillae external to them. Nasals oblong, with the anterior surface > cone 

 Vomer visible near the middle of the palate, in the form of a short, broad loze g 



