A NEW FOSSIL PORPOISE FROM MARYLAND. 175 



Originally it was probably about 20 mm. broad. Viewed from below it is oblong, 

 nearly flat, and not sharply acuminate anteriorly; posteriorly it is divided along 

 the median line by a deep, angular sulcus, which extends forward to the middle 

 point of the length. The internal posterior lobe is angular, while the external 

 one appears to have been globose, and probably did not extend much, if any 

 beyond the internal one. 



Viewed from above, the involution of the inner lip is narrow and sinuous in 

 outline. The interior of the bulla is not distinctly divided into two depressed 

 areas separated by a transverse ridge, as in Schizodelphis , but presents two quite 

 shallow depressions, separated by a wide, flat area covered with small tubercles. 

 The orifice of the Eustachian canal is very broad, as in Delphinus, Phocccna and 

 other recent delphinoids. 



Periotic (PI. XXV, figs. 6, 7).— The periotic is 30 mm. long and 18 mm. broad 

 at the posterior end. It resembles the same bone in Delphinus, Prodelphinus , 

 Sotalia and Phocama in general form, having, perhaps, the closest similarity to 

 that of Delphinus. Viewed from above, the bone is oblong, nearly flat, with 

 truncated anterior end and transverse posterior end, the outline of the latter 

 being rounded, and terminating, of course, in the tympanic process. 



Viewed from within, the petrosal is seen to be only moderately large and to 

 be situated near the middle of the length of the periotic, not strongly inclined 

 forward and with a nearly straight inferior outline. The anterior and posterior 

 process of the periotic from this point of view are of about equal length. Seen 

 from within (or the tympanic aspect) the tympanic process appears as a rounded, 

 slightly concave facet, smaller in diameter than the petrosal. 



Hyoid Bone. 



The hyoid bone (PI. XXV, fig. 5) is nearly complete, the missing parts being 

 the distal end of the right stylohyal, and the middle portion of the left stylohyal. 

 The basihyal is separate from the ceratohyals, on account of immaturity. 



The stylohyals were originally about 90 mm. long, and have a maximum 

 breadth of 15 mm. The mastoid, or proximal, end is elliptical, with the long 

 axis at right angles with the shaft of the bone. The shaft is depressed triangular, 

 flat dorsally (or posteriorly) , and convex ventrally, with the highest part near 

 the external border. This border is slightly convex, while the internal border 



is concave. The distal end, or that which joins the basihyal, is oblique and 

 rounded. 



The basihyal is a thin, irregularly hexagonal bone, about 36 mm. in diameter, 

 with a rather deep anterior emargination, a convex posterior border, and two 

 pairs of articular facets, of which the posterior is the larger. The superior and 

 inferior surfaces are both 



The ceratohyals are 57 mm. long, with a maximum diameter of 18 mm. 

 Ine external border is convex and the internal border arcuate. The ventral 

 (or anterior) surface is nearly flat, while the dorsal is convex. The proximal 

 end is thick and elliptical in outline; the distal end, tapering, thin, and rounded. 



concave. 



