EXPLANATION OF PLATES. 



PLATE 1. 



FIGURE 1. Cranium of the type of Sibbaldius tectirostris Cope. Dorsal view. Philadelphia Academy of 



Natural Sciences. 

 FIGURE 2. Cranium of Balcenoptera physalus (L.). Dorsal view. No. 16045, U. S. National Museum. Cape 



Cod, Mass. Collected by the U. S. Fish Commission. 

 FIGURE 3. Cranium of Balcenoptera physalus (L.). Dorsal view. No. 16039, TJ. S. National Museum. Cape 



Cod, Mass. Collected by the U. S. Fish Commission. 



PLATE 2. 



FIGURE 1. Cranium of the type of Sibbaldius tectirostris Cope. Ventral view. 



FIGURE 2. Cranium of Balcenoptera physalus (L.). Ventral view. No. 16045, U. S. National Museum. Cape 



Cod, Mass. 

 FIGURE 3. Cranium of Balcenoptera physalus (L.). Ventral view. No. 16039, U. S. National Museum. Cape 



Cod, Mass. 



PLATE 3. 



FIGURE 1. Cranium of Balcenoptera physalus (L.). Dorsal view. Cape Cod, Mass. Ward's Natural Science 



Establishment, Rochester, N. Y. 

 FIGURE 2. The same. Ventral view. 

 FIGURE 3. The same. Lateral view. 



PLATE 4. 



FIGURE 1. Cranium of the type of Sibbaldius tectirostris Cope. Lateral view. 



FIGURE 2. Cranium of Balcenoptera physalus (L.). Lateral view. No. 16045, U. S. National Museum. Cape 



Cod, Mass. 

 FIGURE 3. Cranium of Balcenoptera physalus (L.). Lateral view. No. 16039, U. S. National Museum. Cape 



Cod, Mass. 

 FIGURE 4. Bones from the type-skeleton of Sibbaldius tectirostris Cope. Right first rib (double-headed), first 



lumbar, first dorsal, and axis. 



PLATE 5. 



FIGURE 1. Cervical and dorsal vertebrae of the type-skeleton of Sibbaldiiis tectirostris Cope. 

 FIGURE 2. Lumbar vertebrae of the same. 

 FIGURES 3 and 4. Caudal vertebrae of the same. 



PLATE 6. 



FIGURE 1. Ribs of the type-skeleton of Sibbaldius tectirostris Cope. 

 FIGURE 2. Left scapula and humerus of the same. 

 FIGURE 3. Right first rib of the same (double-headed). 



FIGURE 4. Anterior portion of the skeleton of Balcenoptera velifera (?), from behind, showing the ribs, 

 sternum, etc., in position. Coast of California. Wistar Institute, University of Pennsylvania. 



3" 



