1895.] i.06 [Cope 



APPENDIX. 



Mesocetds siPHUNCXJLtis, sp. nov. 



The geuus Mesocetus was established by Van Beneden * for Mysta- 

 coceti in which the posterior part of the mandibular ramus approaches in 

 its characters that of the Odontoceti. That is, the condyle is situated at the 

 middle of the vertically compressed posterior border, and is more or less 

 expanded transversely. It is thus below the superior part of the poste- 

 rior extremity of the ramus, instead of constituting that part, as it does in 

 the whalebone whales generally. That structure is naturally adapted to 

 a more anterior direction of the glenoid cavity, as is shown by Van 

 Beneden. The only known species of the genus is the M. agrami Van 

 Ben. from the Neocene beds of Agram in Croatia, Austria. It is of 

 much interest that a second species is now determined to have existed in 

 the Neocene formation of Virginia. 



Van Beneden does not appear to have seen much if any of the mandibu- 

 lar ramus anterior to the condyle. I have a ramus nearly entire, and 

 smaller parts of three others, and can thus locate the genus Mesocetus 

 in relation to those already defined. In the species now to be described, 

 the ramus has no large dental canal, but it is almost entirely filled with 

 spongy bone of moderate coarseness. The gingival canals unite into a 

 single tube which is not larger than one of the external gingival canals, 

 and which runs about opposite to them or a little distance below the 

 superior edge. In this disposition of the canals Mesocetus diflfers from 

 any of the genera of Mystacoceti referred to in the preceding pages. 



Char, specif. — Founded primarily on a nearly complete right mandibular 

 ramus, and represented by the anterior part of a second ramus of a 

 smaller individual. The distal part of the ramus of a third individual 

 resembles the last one, but differs in some respects from it, so that the 

 reference cannot now be made. These specimens I saw taken Irom the 

 same locality and bed, and I took the type specimen myself piecemeal 

 from the deposit. The latter is a wet phosphatic marl, and it was impos- 

 sible to remove the specimen without damage. It has been reconstructed 

 under my eye by my assistant so as to be in good condition. 



The ramus exhibits little curvature in any direction. It is strongly 

 compressed, and although the external face is more convex than the inter- 

 nal, the convexity is not great. The superior border is throughout 

 thicker transversely than the inferior. Both are obtusely rounded anteri- 

 orly, but both become more compressed posteriorly. The inferior border 

 becomes rather acute posteriorly. The usual ledge is present on the 

 internal or symphyseal side of the distal extremity. The representative 

 of the anterior part of the dental canal issues posterior to the distal 

 border and a little below the superior border ; the external border of the 



*Memoires cle I' Academic royale des Sciences de Lettres et des Beaux. Arts de Belgiqiie 1882, 

 Vol. xlv. 



PUOC. AMER. PHILOS. SOC. XXXIV. 147. T. PRINTED JUNE 13, 1895. 



