ART. 15. A NEW GENUS OF WHALE FROM MARYLAND KELLOGG. 13 



The thinner portion of the invohicrum is distinctly continued for- 

 ward to the anterior hmit of the tympanic cavity; the convexity of 

 the postero-internal portion of the involucrum abruptly subsides, 

 while the anterior portion becomes decidedly concave. The inner 

 surface of the outer lip of the left tympanic is very rugged opposite 

 the convex portion of the involucrum, but this may be due to a 

 pathological condition for the same surface on the right tympanic 

 is perfectly smooth. 



The ventral surface of the tympanic bone (pi. 6, fig. 2a) maintains 

 a more equable breadth from the posterior to the anterior end, the 

 antero-external and the postero-interal angles of which are rounded. 

 The anterior and posterior faces of the tympanic slope obliquely 

 backward from the internal to the external margins. 



The characters derivable from the tympanic bones are sufficiently 

 diagnostic to be used as a guide in the determination of species. In 

 regard to the differences which are observable in the tympanic bones 

 of Parietohalaena, Cetotheriiwi, Idiocetus, and the form under dis- 

 cussion, it may be said that, though seemingly of slight importance, 

 they afford a means of distinguishing the various species. The 

 peculiar features of the two tympanies described above are sufficiently 

 marked to justify their being regarded as belonging to a distinct spe- 

 cies, but nearest allied to Parietohalaena palmeH. There is a strong 

 possibility that these tympanies belong to one of the previously de- 

 scribed fossil cetaceans of the Calvert formation, but no definite 

 allocation will be made until more material is available for study. 



MEASUREMENTS OF THE TYMPANIC BONES. 



tn/tn. 



Greatest length of right bulla 52.5 



Greatest length of left bulla 52 



Greatest width of right bulla 30 



Greatest width of left bulla 30.7 



Greatest depth of right bulla on internal side 29 



Greatest depth of left bulla on internal side 29 



Greatest depth of right bulla on external side (ventral face to tip of 



processus sigmoideus) 40 



Distance from antero-internal end of right tympanic to anterior end of 



involucrum 18.5 



Distance from antero-internal end of left tympanic to anterior end of 



involucrum 19.5 



EXPLANATION OF PLATES. 



Parietohalaena palmeri, new genus and species. Cat. No. 10,668, Division of 

 Vertebrate Palaeontology, United States National Museum. Calvert for- 

 mation, western shore of Chesapeake Bay, 1 mile above Dare's Wharf, 

 Calvert County, Maryland. Collected by William Palmer, August 14, 

 1913. 



