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



The most characteristic of the many skeletal modifications which 

 are exhibited in this group is the formation of more or less complete 

 osseous grooves or funnels for the partial or complete enclosure of 

 'the air-bladder. Such recesses are formed by the transverse processes 

 -of the fourth vertebra, either singly, or in conjunction with those of 

 the fifth vertebra, and vary greatly in depth and in the extent to 

 which they are surrounded by bone. They may be comparatively 

 shallow and widely open on the ventral side, as in Ahysis, Bagarius, 

 and Glyptosternum ; or may take the form of deep, transversely 

 disposed grooves, contracted distally and somewhat expanded proxi- 

 mally (Pimelodus sapo, JEutropiichthys, and Schilb'ichthys) ; or they may 

 partake of the nature of transversely arranged bony cylinders or 

 funnels, open distally in the dry skeleton, but otherwise with more or 

 less complete osseous walls (Glarias, Gallomystax^ and Cetopsis). The 

 transverse processes of the fourth vertebra always form the dorsal and 

 anterior walls of the recesses, and sometimes furnish, in addition, a 

 posterior wall, or even incomplete ventral walls ; rarely do they com- 

 pletely enclose tubular recesses (Cetopsis)'; more frequently the 

 'posterior walls are formed by the transverse process of the fifth 

 vertebra (Glarias, Callomystax). Exceptionally, a slender, lateral, 

 bony outgrowth from each of the longitudinal ridges bounding the 

 aortic groove in the region of 'the complex centrum may become 

 attached to the ventral wsdl of the corresponding lateral air-sac 

 ' (Glyptosternum, Bagarius) ; or, as in one instance (Glarias), the out- 

 growths may be strongly developed and form no inconsiderable 

 portion of the ventral walls of the two osseous funnels. Ventrally, 

 the shallow recesses may be closed by a tough fibrous membrane which 

 also invests the corresponding walls of the contained air-sacs (e.g., 

 Bagarius) -, and by "the same means vacuities in the walls of the more 

 complete bony funnels are entirely closed (Glarias, Gallomystax). The 

 formation of a horse-shoe-shap-ed recess by the transverse processes 

 ot the fourth and fifth vertebrae in conjunction with plate- like lateral 

 outgrowths from the aortic ridges, which is open laterally and behind 

 in the dry skeleton, occurs only in one genus (Ailia). In whatever 

 way the osseous recesses or capsules may be formed they are almost 

 always open laterally or distally in the dry skeleton, and closed by 

 lateral cutaneous areas in the fresh specimen. 



The condition of the air-bladder in this group is singularly varied, 

 and in proportion to the bulk of the Fish is always extremely small. 

 Many of its most characteristic features are clearly the results of 

 atrophy and degeneration. The principal modifications appear to be 

 due to the partial or complete suppression of the lateral chambers and 

 the subdivision of the anterior chamber into two laterally situated 

 cavities or air-sacs, either by the solidification of the mesial portion 

 of the bladder or by more or less complete longitudinal constriction. 



