450 DRIVER— THE LUCIOPIMELODIN^. 



in excess of the length. In Rhamdia it extends to the ninth vertebra 

 while in Pimclodclla and Pimelodus it extends only to the eighth. 



As stated, the lateral processes of the first five vertebrae in the 

 Pimelodinse are coalesced and form a more or less smooth roof be- 

 neath which the air-bladder lies. In Rhamdia (Plate II, Fig. B) 

 the transverse processes are quite distinct, and are separated from 

 each other ; the coalescing is more complete in Soruhiiim, Heniiso- 

 ruhim, Pimelodella and reaches the climax in Pimelodus. 



ABC 



Text- Fig. i. A, Air-bladder of Sorbium lima; B, Air-bladder of Rhamdia 

 cinarescens ; C, Air-bladder of Pimelodus clarias. Outlines as seen from 

 below. 



The air-bladder of Pimelodus is small. The coalescing of the 

 vertebrae is more complete in this genus than in others. The outer 

 edge of the shield formed by the coalesced process has a tendency to 

 become arched antero-posteriorly. 



The air-bladder in all these genera comes in close contact with 

 the skin which serves as a tympanic membrane. This can be seen 

 especially well in young specimens. 



Perugia (Plate 11,^, C,D,E), which had hitherto been placed in 

 the Pimelodinae, has the air-bladder very much reduced in size, con- 

 stricted longitudinally with one lobe on each side of the centra of the 

 coalesced vertebrae. Each lobe is surrounded by a partial capsule, 

 made up of the coalesced vertebrae above and behind, the scapula 

 and the process connecting the scapula with the basioccipital in 

 front. The floor of the capsule is membranous. 



