ART. 19 A MIOCENE PORPOISE FROM MARYLAND — KELLOGG 27 



Measurements of the left periotic (in millimeters) 



I'.i-eadth of periotic at level of Fenestra ovalis (as measured from ex- 

 ternal face above groove to internal face of pars cochlearis) 16.9 



Greatest length of perioUc (tip of anterior process to tip of posterior 



V , 2S. o 



process) 



(Jreatest dorsoventral depth of periotic (as measured from most in- 

 flated portion of tympanic face of pars cochlearis and groove to most 

 projecting point on cerebral face) ^0- 5 



Distance between Fenestra rotunda and tip of anterior process 16.7 



Distance between Fenestra rotunda and tip of posterior process---- 15.5 



Distance between epitympanic orifice of Aquaeductus Fallopii and tip of 

 anterior process 



TYMPANIC 



After preparations had been made for the removal of the left 

 tympanic bulla from the mounted specimen for study, it was found 

 that the thin outer lip was badly fractured. The bone was removed 

 as carefully as possible, but unfortunately a few small pieces were 

 missing and no contact could be secured between the sigmoid process, 

 the processus anterior of the malleus, and the accessory ossicle or 

 uncinate process with what remained of the thin outer lip. The 

 right tympanic and periotic remain attached to the skull. 



On comparing the external surfaces of this tympanic bulla (pi. 1, 

 tig. 3) and that of Prodelphinus malayanus, it was interesting to 

 note hoAv differences in proportions modify the general appearance 

 of these bones. It is to be regretted that no comparisons could be 

 made with tympanies of the living porpoise Sotalia. According to 

 Van Beneden's figures of the tympanic bulla of Sotalm guianemh, 

 the proportions of these bullae appear to be essentially the same when 

 viewed from the external side; the shape of the involucrum is similar 

 and the curvature of the dorsal profile is almost identical. This 

 fossil tympanic buha is slightly larger than that of Prodelphinus 

 malayanus, but the thin outer lip is relatively deeper and the superior 

 border of the lip does not curve inward as abruptly. When viewed 

 from the external side the posterior margin is seen to be less rounded 

 than in Prodclphinm, the posterior apophysis is slightly larger, and 

 the tympanic bulla as a whole is relatively deeper. The sigmoid 

 process of this tympanic bulla is not complete, but it is entire on the 

 opposite one ; the posterior border and extremity are greatly thick- 

 ened as in Prodelphinus malayanus and the terminal end is twisted at 

 right angles to the basal portion. In front of the sigmoid process 

 there is a distinct crease extending obliquely across the external sur- 

 face of the thin outer lip from the superior to the inferior margin. 

 The posterior conical apophysis is rather large, but otherwise tlie 



