482 MR. R. I. FOCUCK UK THE 



Ictonyx is like Mellivora except that there is no crest behind 

 the partition on tlie inner wall of the bulla; and the related 

 genus Pcecilictis only differs in the greater size of the supple- 

 mentary chamber in the periotic and of the space above the 

 tympanic ring. 



Taxidea is like Pcecilictis. In confoiinity with the great 

 inflation of the bulla the space between its roof and the tympanic 

 ring is very high and septate. The posterior i-after is continuous 

 with the posterior edge of the tymjoanic ring, and descends so low 

 that only a small passage is left between its inferior arcuate edge 

 and the periotic. A posterior chamber is thus cut off almost 

 as completely as in some ^luroids. This posterior chamber is 

 extended anteriorly above the tympanic ring on the inner side of 

 the stylomastoid foramen, and it communicates hj a. wide passage 

 with a large cavity, larger than in Mellivoi-a, hollowed out in the 

 periotic between the mastoid and paroccipital processes. 



Thus the bulla of Taxidea is very different from that of Meles, 

 and not essentially like it as Flower stated. It is much more 

 like that of Mellivora, although the partition is better developed 

 and the periotic hollow much larger. In Mellivora, too, the 

 posterior chamber is not extended forwards above the tympanic 

 ring on the inner side of the stylomastoid. 



In Grisonella (sp. from Cordova in the Argentine) the roof of 

 the bulla is depressed on to the tympanic ring, and fused with it 

 practically throughout its extent except for the presence of one 

 or two very small cellular spaces in front and behind. The 

 anterior rafter is very large, and lising from the summit of the 

 anterior part of the tympanic ring, descends obliquely downwards 

 and inwards, dividing the anterior part of the cavity, which is 

 further broken up by anastomosing ridges, into an upper and a 

 lower portion. Just behind the posterior end of the ring but 

 confluent with it arises a comparatively large arched rafter which, 

 crossing the loof, descends along the inner wall of the bulla, 

 dividing the cavity into an anterior and posterior chamber 

 which comrnunicate by a comparatively narrow passage above the 

 periotic. The posterior chamber has septa on the inner wall and 

 anastomosing ridges on the floor, and anteriorly just behind the 

 main transverse septum formed by the posterior rafter there is a 

 passage by which the iiosterior chamber opens into the hollowed 

 external portion of the periotic. The floor of this hollow is 

 uneven with ridges and shallow pits. 



It is interesting to note that the bulla of Grisonella is widely 

 difterent from that of Tayra, although the two genera were 

 formerly regarded as identical. In possessing a hollowed periotic 

 chamber communicating with the cavity of the bulla, Grisonella 

 resembles Mellivora, Ictonyx, and Taxidea, and is further like the 

 latter in the origin of the posterior rafter from the posterior end 

 of the tympanic ring. But in none of these genera is the ring 

 confluent with the rOof of the bulla as it is in Gi^isonella. 



A skull of Lyncodon, with a broken bulla, in the Bi'itish 



