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Profs. T. W. Bridge and A. C. Haddon. [June 20, 



merit to the ventral surface of the complex centrum evidently corre- 

 sponds to the skeletally attached medio- dorsal portion of a normal 

 anterior chamber (e.g., Pimelodus pulcher). Whether this inter- 

 mediate tubular portion be present or absent, the inner portion of the 

 anterior wall of each air-sac is always attached to the contiguous 

 lateral surface of the complex centrum, or to the radial nodule, or even 

 to both, after the fashion of the anterior pillars of the normal bladder. 

 Occasionally also, as in such normal forms as Arius, the outer stratum 

 of the anterior wall of each air-sac may be dorsally conuected with 

 the decurved anterior margin of the transverse process of the fourth 

 vertebra (e.g., Bagarius, Glypiosternum) . 



As a rule, where the air-bladder is more completely surrounded by 

 its osseous capsules, the rigid skeletal attachments of the former are 

 not so obvious as in those cases in which the bony investment is but 

 partial. 



The relations of each lateral cavity or air-sac to the crescentic 

 process of the tripus imbedded in its dorsal wall are almost precisely 

 the same as in each half of the anterior chamber in a normal Siluroid. 

 The convergence of the fibres composing the anterior, lateral, and 

 dorsal walls of each air-sac, and their insertion into the crescentic 

 process of the tripus, takes place in nearly all the forms included in 

 the present group, but in two or three instances (e.g., Glyptosternum) 

 the dorsal wall has partially or completely atrophied, or at all events 

 has so far degenerated that it is extremely improbable that its fibres 

 can possibly exert any pull upon the tripus as the result of any dis- 

 tension of the air-bladder. 



Radial fibres are always present, but in some cases are less obviously 

 specialised than in others, and, where radial nodules are absent, pass 

 directly from the lateral surfaces of the complex centrum to the 

 inner or concave margins of the crescentic processes of the tripodes. 



Broadly speaking, it may be affirmed that the skeletal attachments 

 of the air-bladder in the Siluridse abnormales, both to rigid portions 

 of the skeleton and to movable ossicles, are in substantial agreement 

 with those of the anterior chamber of the S. normales. 



The Weberian ossicles undergo but slight modifications in the 

 different members of this group. Claustra are occasionally absent, 

 and even when present are but feebly developed spicules of bone. As 

 a rule, the scaphium has no ascending process, bat only spatulate and 

 condylar processes. The intercalarium may be absent, in which case 

 the interossicular ligament is extremely short, or represented by 

 a very small nodule in the usual position ; horizontal and ascending 

 processes are invariably wanting. The tripus is very variously 

 modified. A ventral ridge is rarely present. The crescentic process 

 may be curiously angulated and heeled (Clarias) ; nearly straight 

 with a pointed posterior extremity (e.g., Bagarius) ; or but slightly 



