NATURAL SCIENCES OF PHILADELPHIA. 185 



remaining centrum. One extremity of the vertebra is flat, the other strongly- 

 convex, and none have any trace of diapophyses. The neural arches have been 

 partly broken away, but have been similar to those of other genera, while the 

 groove that marks the inferior aspect of caudal vertebrae is normal. In two 

 vertebrae, the longest and shortest, the foramina which usually pierce the sides of 

 the centra vertically, issue below, within the basal groove and above, below and 

 outside the basis of the neurapophysis. In another specimen the foramen 

 opens outside the inferior sulcus, and in one there is no foramen at all. These 

 structural features indicate a genus of general peculiarity, and perhaps allied 

 to Basilosaurus. There may be some question as to whether two species are 

 not represented among the vertebrae. 



CeTOPHIS HETEROCLIT0S CopC. 



The four specimens may represent a proximal, a median, and a distal caudal 

 of one individual, and a median caudal of another. They were not adult, as 

 the epiphyses are entirely separable. The longer or proximal caudal is sub- 

 hexagonal in section, the median depressed, and the smallest round in section. 

 The larger median is nearly round in section. The epiphysis instead of re- 

 treating before a process of the centrum opposite the four apophyses, as in 

 Ixacanthus, advances on the centrum at these points. The inferior groove of the 

 centrum is deep on the first and shallower on the succeeding ; obsolete on the 

 last. The neural canal about as large on the proximal as in anterior caudals 

 generally. 



Length longest 



Height flat articular face 



Width do. do 



Length median (smaller) 



" without epiphyses 



Height flat face 



Width " 



Length median (larger) 



Width flat f\ice 



Length smallest 



" without epiphyses 



Height flat extremity 



Width do. do 



From Charles county, Maryland. From Jas. T. Thomas, Mus. Academy. 



The convex articulation of the vertebr;e would suggest a greater flexibility 

 of the column in this part than is usual among Cetacea, but more as in cervi- 

 cal vertebra; of long-necked mammals, and in reptiles. The absence of dia- 

 pophyses would confirm such an indication. Were it not for the inferior groove 

 the longer vertebrte above described might be taken for a lumbar, and it may be 

 such, as in the Zarhachis flagellator a similar form coexists with the 

 usual form of'diapophysis of that part of the column. There is probably some 

 distant affinity between the two genera. 



With respect to the genus Basilosaurus, it may be noted that the Polppty- 

 ehodon tuierruptus of Emmons, must be regarded as established on one of its 

 canines. Whether the species be the D. cetoides must be left for their 

 examination. A fine specimen is in the Museum of the Mount Holly Lyceum 

 of Natural History. 



In the description of the Cynorca proterva (in Proceed. Acad. 186Y,) mis- 

 led by the extraordinary resemblance to Giebel's plate quoted, I unfortu- 

 nately mingled with its molar and premolar teeth, the canine of small Dico- 

 tyles. This point, suggested to me by Leidy, I have no doubt is the case. It 

 will be necessary therefore to add the following details of character of the 

 characteristic molar and premolar, which I described too briefly (p.*I51) : "Mo- 

 lar with two roots. Premolars with short conic crowns. Premolars compressed, 



1868.] 13 



