Cla.ffiijirution of the Ordtr Ostar'iophyU. 569 



The genera may be arranged thus : — 



I. Gill-cavity with an accessory air-sftc, which extends backwards 

 into the tail; dorsal liu short; uo adipose tin. 



Sacciibranchus. 



ir. Gill-cavity -svith a diverticulum contaiuing a dendritic accessory 

 liraiiohiul orj.'-an attached to tlie second and fourth branchial 

 aiches ; dorsid liu more or leas elongate. 



A. Au adipose fin JItterobranchus, Dinotopteriis. 



W. \o adipose fin ; dorsal nearly or quite reaching the caudal. 



Plates at side of head connected .... Clarias. 

 Plates at side of head reduced, separated 



by an interspace Allnhenchclys, C'nrrialahes, 



Gyinnallabes, Channalabes. 



Saccobranchns often placed in a separate group, is pre- 

 cisely similar to C/arias in osteologieal characters. The 

 plates protecting the sides ot" the head are present in all the 

 members of the family, and 1 have satisfied myself that 

 IJoulengcr's statement to the contrary for the degraded 

 genera allied to C/arias is erroneous. 'J'hese plates are 

 present in most Siluroids, but not so strongly developed ; 

 the anterior belongs to the circumorbital series, the posterior 

 transmits the lateral line to the proeoperculum. 



Family 14-. Pangasiidae. 



The Indian genus Pangasius differs from tlie Bagridae 

 externally in the long anal fin, \vith28 to 40'rays; maxillary 

 and one pair of mandihulary barbels are present, but no 

 nasal barbels. The skeleton is very similar to that of 

 generalized Bngrida?, differing only in the development of 

 an elastic spring mechanism, the anterior rami of the para- 

 ])Ojihyses of the fotirth vertebra being expanded distally to 

 form a pair of oval plates inserted in the anterior wall of 

 the air-bladder, but free from the supra-eleithrnm. The 

 air-bladder consists of an anterior division, corresponding 

 to a normal bladder, and of a posterior tubular caecum. 

 Vcrtebrce 15 + 29. 



Family 15. Synodontidae. 



External characters of the Bagridaj, except that the gill- 

 membranes are confluent with the skin of the isthmus ; the 

 nostrils may be close together or wide apart and there is no 

 nasal barbel ; the pelvic fins are 7-rayed. There is a broad 

 nuchal sliield with parallel edges ; the epiotics are small, 

 liidden beneath the supraoccipital ; pterygoid and meso- 

 pterygoid are absent ; there is no post-temporal ; the upper 



Ann. & May. N. Ilist. Ser. 8. Vol. viii. 38 



