1896.] 14:5. [Cope. 



In the interstices of the specimen portions of matrix remain which 

 have the color and character of the material of the Yorktown forma- 

 tion. Embedded in this at certain points are fragments of Molhisca of 

 the genera Pecten, Lncina and Turritella. It was probablj^ derived from 

 the Chesapeake region. The fragment belongs to the museum of Johns 

 Hopkins Universitj'. oi^ Baltimore, and I am under many obligations to 

 Prof. William B. Clark, State Geologist of jVIarjdand, for the opportu- 

 nity of studying it. 



Rhegnopsis pal^^atlanticus Leidy. Balcena paUeatlantica, Proceeds. 

 Academy Phila., 1851, p. 308. Bulmnoftera jjalceatlantica Cope, 

 Proceeds. Academy PMla., 1868, p. 193. I^'otobala>na palmatlantica 

 Leidy, Extinct Mamm. Dakota, Nebraska, 1869, p. 440. 



The typical and only specimen of this species is a fragment of a lower 

 jaw from the Yorktown bed of S. E. Virginia. Its specific characters 

 ditier from those of other BalaMiidne referred to in this and preceding 

 papers by me, and it displays in addition a character which Leidy has 

 described, and which is very conspicuous. That is, the presence of a 

 Meckelian fissure, which extends deeply into the mandibular ramus. I 

 agree with Leidy that this feature should be regarded as generic, and so 

 define the genus as follows, under the name Rhegnopsis. Roof of dental 

 canal perforated by gingival tubes ; a ]\Ieckelian fissure. Dr. Leidy's 

 name Protobahtna is preoccupied by Van Benedeu (1867). 



Cetotherium leptocentrum. Eschrichtius leptocentrus Cope, Pro- 

 ceeds. Academy Phila., 1867, p. 147. Cetotherium leptocentrum Cope, 

 American Naturalist, 1890, p. (iKi. Cetotherium crassangulum Co\ie, 

 Proceeds. American Philosoj)hical Society 1895, ji. 148. 



After the latest description of this species was published I visited 

 the locality at which it was discovered, in companj^ with Prof. Arthur 

 Bibbins, of Baltimore. I found a ]iart of a mandibular ramus which 

 coincides in all respects so closelj' with the portions which are still 

 adherent to the skull that I have no doubt that they pertain to the same 

 species, and probably to the same individual. One character in which 

 this fragment agrees with the other portions of the rami is the presence 

 of coarse cancellous bony tis.sue throughout the gingival dental canal. 

 This reduces the diameter of the latter to that of the large external 

 gingival canals. The form of the middle part of the ramus as indicated 

 by the fragment is very different from that of any other whalebone 

 whale known to me. The internal face is nearly flat and vertical, while 

 the external face is convex only at the superior portion. For a short 

 distance exterior to the superior angle it is subhorizontal ; it then 

 gradually decurves, and is then entirely flat to the inferior sul)acute 

 edge. Tlie section is then subtriangular, with the base superior and the 

 apex inferior. The interior gingival foramina continue very small, and 

 they are not connected by a groove. Distance between two of them, 



