170 A NEW FOSSIL PORPOISE FROM MARYLAND. 



of the orbit almost touches the extremity of the zygomatic process. In conse- 

 quence, the original form of the supraoccipital cannot be accurately determined. 

 The superior border was, however, evenly rounded, and did not overhang the 

 vertex. The surface is concave in the median line, with no trace of a ridge. 

 The posterior borders of the temporal fossae were widely separated, as in recent 

 delphinoids. 



The occipital condyles are small, widely separated above, but approximated 

 below, where the interval between them is only 15 mm. Their surface is some- 

 what pitted, indicating that the individual is immature. 



Mandible (PL XVIII, figs. 2 and 3). — The mandible is large compared with the 

 size of the cranium, and the rami less slender than in many recent species of 

 Delphinus, Sotalia, etc. The superior border is quite evenly concave from the 

 anterior extremity to the coronoid process. The inferior border is concave 

 in the proximal two-thirds, and convex distally. The ramus is slenderest at the 

 middle of the length of the jaw. The coronoid region is especially elevated, the 

 distance between the coronoid process and angle amounting to more than one- 

 fourth the total length of the jaw, while in recent species of Delphinus, Sotalia, 

 and Steno it is much less than one-fourth, or even less than one-fifth. The 

 symphysis is very long, being almost exactly one-third the length of the jaw. 

 The conformation of the proximal end of the jaw internally is similar to that of 

 recent delphinoids, except that the extremity of the coronoid process is concave, 

 with a channel running forward immediately below the superior border of the 

 jaw and reaching nearly to the tooth-row. The angle is lacking on both sides of 

 •the mandible, but appears to have extended nearly to the line of the condyle. 

 The border of the jaw immediately in front of the angle is curved inward and 

 very thin. The condyle is small and elliptical, with the long axis vertical. 

 The margin of the j aw from the top of the condyle to the extremity of the coronoid 

 process is nearly straight, the process itself not being recurved, as it is in many 

 recent delphinoids. 



The superior surface of the symphysis is narrow and nearly horizontal. On 

 the outer side of the ramus, opposite the symphysis, are several large foramina, 

 from each of which a canal extends some distance forward. There is, however, 

 no distinct channel near the inferior margin of the j aw, as in Cyrtodelphis , Plata- 

 nista, Stenodelphis , etc. One rather large elliptical foramen is situated about 

 in line with the middle of the tooth-row. 



Measurements of the Skull. 



Min. 



360 



Total length of skull 



Greatest breadth across zygomatic processes '..'.'.'..'. *!!? 



Breadth across centers of orbits 155 



Breadth of rostrum at maxillary notches 92 



Breadth of premaxillae at same point " 57 



Breadth of rostrum at middle 36 



Breadth across premaxillae at same point '.'.'.'.'.'. '. '. '. '. l8 



Greatest breadth between outer borders of premaxilla opposite 92 



nares 



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