SKELETON AND LAETNX OF XENOPUS AND PIPA. 121 



Boulenger, 3. p. 432, and others) that in Pelohates and some 

 ■otlier genera the intervertebral sphere may remain free in the 

 adult, or may attach itself indifferently to the vertebra in front 

 or that behind, causing them to become procoelous and opistho- 

 coelous respectively. The extent of ossification of the fronto- 

 parietals is a character upon which Cope lays considerable stress 

 in his classification. In Pipa and Xenopus the degree of ossifi- 

 cation of the roof of the skull rather negatives their affinity with 

 the Discoglossidse, to which Cope (7. p. 248) considers them 

 most nearly allied. The frontoparietal is strongly ossified in 

 PalcBolatrachus. In both Pipa and Xenopus the epicoracoid 

 cartilages of the shoulder-girdle are in contact in the middle line, 

 without overlapping or fusing, so that in this respect the Aglossa 

 occupy a position intermediate between the Arcifera and the 

 Firmisternia. There is no ossified xiphisternum, nor omo- 

 fiternum, and Cope regards the girdle, although a rigid one, as a 

 modified variety of the arciferous type. Since the firmistern 

 Anura are arciferous in early life, and since the girdle of Pipa 

 and Xenopus cannot be conceived as originating by any modifi- 

 cation of the raniform type, the probability of any affinity between 

 the Aglossa and the firmistern Phaneroglossa is empbatically 

 negatived. 



In the limb skeleton tbe distal carpalia 3 and 4 are perfectly 

 distinct in both Xenopus and Pipa (23. p. 161). This is a 

 primitive character which brings the Aglossa near to Pelohates 

 and the Discoglossidse. But, on the other hand, the reduction 

 of the skeleton of the pollex in Xenopus and Pipa, and the fusion 

 of the second and third tarsalia of the distal row, are features 

 indicating a degree of specialization not paralleled in the Disco- 

 glossidse, Pelohates or Pelodytes. In the fusion of the ulnare 

 with the postaxial centrale, Pipa differs not only from Xenopus 

 but from all other Anura (23. p. 161). Xenopus possesses 

 maxillary teeth, while Pipa is edentulous ; but assuming that 

 Cope is justified in discrediting the systematic value of the 

 tooth-characters in Anura (7. p. 247), another great barrier 

 between Pipa and Xenopus is broken down. 



The extraordinary brood-pouches on the back of the female 

 Pipa are not represented in Xenopus ; but they cannot be 

 regarded as of taxonomic importance, since brood- chambers of 

 one kind or another are developed independently in widely- 

 removed genera of Anura. The abnormality, amounting almost 



