NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 21 



degree it resembles Rhachioncctes, but appears to differ in having a 

 considerably more reduced nasal, like the higher Balaenopterines. 



Cetotherium, also from the Tertiary of Europe and presumably of 

 America, which is likewise known from scarcely anything else than 

 the skull, is a very near relative to Plesiocctus. It is slightly more 

 specialized, with the articular surface for the lower jaw on the 

 squamosal pushed somewhat further backward, pressing more against 

 its surroundings, and covering the mastoid ; but otherwise it scarcely 

 differs except in trifles. 



As a pronounced contrast to Rhachioncctes the genus Balccnoptera, 

 on the other hand, stands much higher : with much smaller nasal ; 

 with intermaxillary and maxillary more broadened in front ; with 

 broader and flatter supraorbital process ; with more telescoped brain- 

 case in the median upper part of which there shows itself only a little 

 of the frontal ; with larger, more forward-slanting supraoccipital ; 

 with the articular surface for the lower jaw on the squamosal pushed 

 much further backward, wholly covering the mastoid and shoving 

 the exoccipital more to the rear ; with bony palate strongly lengthened 

 liackward ; with point of attachment for the neck muscles on basal 

 part of occipital compressed, flattened ; with the basioccipital more 

 shaped to the larynx and gullet ; with the skin under the floor of the 

 mouth cavity thrown into longitudinal folds ; with a dorsal fin ; with 

 the hand more lengthened ; with frequently more phalanges in the 

 median fingers. 



Magaptcra stands yet higher than Balccnoptera. Its body is 

 relatively not much elongated, a fact which points to its origin among 

 the most primitive species of Balccnoptera. But in the structure of 

 the fore limb it has reached far beyond its relatives. On account of 

 some special use or other, perhaps most likely from rapid t^irning 

 about in the water, the arm has grown to an enormous length. The 

 forearm has become very much stretched out, and the hand is yet 

 more conspicuously lengthened, the number of phalanges in the third 

 and fourth finger increased in addition. The scapula has lost both 

 the coracoid process and the crest. 



Balaenidae." 



I. Intermaxillary and maxillary narrow anteriorly, not flattened. 

 Balcsnini. 



A. Mandible slender. Ribs not broad. First metacarpal 



present. 

 Balccna. 



B. Mandible robust. ]\Iost of the ribs broad. First 



metacarpal absent. 

 Ncobalccna. 



