ART. 14. 



MARYLAND FOSSIL PORPOISE — KELLOGG. 



35 



is borne upon a relatively long flattened neck which is strongly con- 

 stricted behind the capitulum. The tuberciilum and capituliim are 

 relatively small. The second rib (pi. 16, fig. 2) is longer than the 

 first, with narrower shaft and neck. The capitulum is larger than the 

 tuberculum. The third rib is characterized by a longer shaft and the 

 neck, while flattened, is even thicker than the second. 



The angle formed by the neck with the shaft of the succeeding ribs 

 becomes less and less acute until in the posterior ones it almost dis- 

 appears and the ribs are regularly curved. The ninth and tenth ribs 

 (pi. 15, fig. 4—5) retain only vestiges of the angle in the form of a 

 slight swelling below the fused tuberculum and capitulum. 



The fourth, fifth, sixth, and seventh ribs are all very much alike. 

 The differences consist of a constant narrowing of the shaft at the 

 angle as we go backward from the fourth (pi. 16, fig. 3) to the seventh 

 ribs, and in addition there is a tendency toward the lengthening of the 

 interval between the capitulum and the tuberculum. The seventh 

 rib (pi. 15, fig. 2) is larger and heavier than any of the others. 



In this fossil porpoise the long necks and the distinct capitula do 

 not disappear until the eighth rib (pi. 15, fig. 3) and up to this point 

 are well developed. Upon the eighth rib the tuberculum and capi- 

 tulum disappear as separate facets. The posterior face of this single 

 facet on the eighth and ninth ribs is indented by a well-marked con- 

 cavity. The position of this concavity suggests that the neck has 

 been shortened and in consequence the capitulum and the tuberculum 

 have coalesced. If this determination is cprrect, then the capitulum 

 has not been lost as some writers have held. The eighth and ninth 

 ribs are very much alike except that the former is more convex. The 

 shaft of the tenth rib does not curve as much as the anterior ribs. 



Measurements of ribs (in millimeters). 



Total lenqrth in a straight line 



Greatest breadth at ane;le. . . 



Greatest breadth at inferior 

 extremity 



Distance between external 

 mar^n of tubercle and 

 head 



Greatest thickness of rib near 

 the middle 



Greatest thickness at the in- 

 ferior extremity 



430. 482. 

 32.0 30.0 



25.0 13.5 



62.5 65.0 

 18.5 17.5 



5.0 



4.5 



466.0 

 29.0 



14.0 



65.0 



19.5 



4.5 



W 



419.5 

 22.0 



t26.0 



18.5 



3.0 



:?; 



407.5 

 22.0 



14.0 



t23. 5 



18.0 



3.5 



344.0 

 22.0 



16.0 



t22. 5 



15.5 



5,5 



* As preserved, incomplete. 



t Breadth of articular face. 



