54 SYSTEMATIC PALEONTOLOGX 



according to Leidy, ' directed upward and moderately forward.' In the 

 T. tuccatus they are directed forwards horizontally, and very little 

 upwards." Cope, 1895. 



Occurrence. — Chesapeake Group. Maryland or Virginia. 



Collection. — Johns Hopkins University. 



Genus BALAENOPTERA Dacep. 



Balaenoptera sursiplana Cope. 

 Plate XXIV, Fig. 2. 



Balaenoptera sursiplana Cope, 1895, Froc. Amer. Philos. Soc, vol. xxxiv, p. 151. 



Description. — In describing this species Cope says : " On comparison 

 with the Balasnopterse described by Van Beneden, it is to be observed 

 that they [the tympanic bones] all differ from the present form 

 in the convexity of superior face, where the dense layer or lip has a 

 different chord or face from that of the space which separates it from 

 the internal longitudinal marginal angle. In the B. sursiplana there 

 is but one superior plane from the eustachian orifice to the internal 

 edge, which is absolutely flat. In all these species also the dense layer 

 of the lip is reflected on the superior edge of the external thin wall at 

 its anterior end. In the present species this layer is reflected in a very 

 narrow strip underneath the free border, which overhangs it. In all 

 these species also the anterior extremity, as viewed from above or below, 

 is angulate, the angle marking the end of the inner border of the dense 

 layer or lip. In B. sursiplana the anterior extremity, viewed in the 

 same way, is truncate. The species which appears to approach nearest 

 is the B. definita Owen, which is figured by Lydekker.' This otolite 

 appears to be flatter above than the species described by Van Beneden 

 although the figure is not clear in this respect. It has the oblique 

 upwards and backwards looking face at the posterior extremity, which 

 is a conspicuous feature of the B. sursiplana, although it is not so 

 sharply defined by a strong transverse convexity of the superior surface, 

 as in the latter. Nor is there as strong a bevel of the anterior extrem- 

 ity of the superior face when viewed from within, as in B. definita. An 



' Quar. Jour. Geol. Soc, London, 1887, vol. xliii, p. 11, pi. ii, tig. 3.- 



