MARYLAND GEOLOGICAL SURVEY 00 



equally conspicuous difference is to be seen in the form of the inferior 

 wall. According to Lydekker, this surface, when the bulla is viewed 

 from within, consists of three planes separated by rounded angles, of 

 which the median is longer than those at the ends. In the B. sursi- 

 plana this surface is regularly convex from end to end. In size this 

 species is like that of the large Balaenopterffi, including the B. definita. 



Measurements. 



ram. 



Axial length of bulla 98 



Width at posterior extremity of anterior hook at superior 



border 71 



Width at anterior extremity of orifice 35 



Width at posterior extremity of orifice 53 



Depth at middle (about) 55 



Greatest depth of lip 38" 



Cope, 1895. 



Occurrence. — Chesapeake Group. Maryland or Virgina. 



Collection. — Johns Hopkins University. 



Genus BALAENA Dinn. 

 Balaena affinis Owen. 



Balaena affinis Owen, 1846, A History of the British Fossil Mammals and Birds, 

 London, p. 530, fig. 231. 



Description. — In describing several specimens of ear bones of whalco 

 from the English Tertiary the author says : " One of the most com- 

 plete of the fossil tympanic bones, which measures five inches in length, 

 resembles the Bat. antarctica in the slight elevation of the outer part of 

 the involuted convexity, and its gradual diminution to the Eustachian 

 end of the cavity; it resembles both Balcence in its traceable con- 

 tinuation to that end, and in the gradual continuation of the 

 concave outer Avail from the involuted convexity; this convexity is 

 indented also, as in both recent Balsenfe, by vertical fissures narrower 

 than the marked indentation which distinguishes the Bal. mysti- 

 cetus. . . . The upper surface of the bone maintains a more equable 

 breadth from the posterior to the anterior end, the outer angle of 



