62 



variations extend in some cases to anomalies," yet it appears to me 

 that, in their number and disposition, they afford to a certain extent 

 sufficiently trustworthy indications of affinity for the classification of 

 the species into several natural groups or families, and which, aided by 

 other characters, would come, without being too elaborate, very con- 

 yeniently within the compass of this primary treatise. 



Somewhat contrary to modern practice, I head the following tabular 

 classification of the Order Cetacea with the Family Platanistidae, prin- 

 cipally in obedience to the dental formula, and partly because of the 

 many connecting forms of organic structure, which ally the members 

 of this family with those of the two preceding orders Zeuglodontia 

 and Sirenia, on the one hand, and with the true Delphinidae, their natural 

 successors in the Cetacean line of affinity, on the other. 



The known individuals of this fresh-water group approach the 

 extinct carnivorous whales by their elongated head, of which the man- 

 dible exhibits a lengthened symphysis ; by their teeth firmly set in 

 both jaws, the anterior ones retaining their prehensile character, while 

 the posterior have their summits worn down broadly to their bases, 

 the latter occasionally exhibiting two short fangs, a dental feature very 

 exceptional among other existing whales. 



They resemble the Manatee and the Dugong in possessing a com- 

 paratively long neck, of which the vertebrae are all free ; in bearing the 

 cartilaginous costo-sternal ribs ; in the peculiar mode of attachment of 

 the ribs to the dorsal vertebrae ; and in the sternum being composed of 

 one piece. 



The Inia, moreover, presents further corroborative affinities to the 

 Sirenia worthy of notice, namely, in the restricted number of the 

 lumbar vertebrae and the singular form of the cervical vertebrae and 

 of the sternum, these important parts being in their structure very 

 unlike to the corresponding ones of any other cetacean, yet strongly 

 recalling to mind those borne by the Dugong and Manatee respectively. 



"With the Delphinidae the alliance is equally well marked the small 

 head, proportionate to the bulk of the body ; the narrow, prolonged 

 beak, parallelled in a less exaggerated form by some individuals of the 

 genus Steno ; the two jaws of nearly the same length and breadth, 

 and both armed with numerous trenchant teeth, the form of which in 

 the Inia greatly strengthens the affinity with several species of the 

 true dolphins, by having the surface of their crowns distinguished by a 

 marked rugosity, a singularity not only indicated clearly in the teeth 

 of some species of the genus Steno, but seen in a lesser degree in those 

 of the young of Orca and Pseudorca. 



And in their manner of living and seizing their prey, no one can 

 dispute the near relationship which exists between the Marine and 

 ITluviatile Dolphins. 



It is to be understood that the number, position, and nature of the 

 teeth are taken from the adult animal only. 



