Classification of the Order Ostariophysi. 569 



The genera may be arranged thus : — 



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

 into the tail ; dorsal tin short ; no adipose fin. 



8accobranchus. 



ir. Gill-cavity with a diverticulum containing a deudritic accessory 

 branchial organ attached to the second and fourth branchial 

 arches ; dorsal fin more or less elongate. 



A. An adipose fin Heterobranchus, Dinotopterus. 



B. No adipose fin ; dorsal nearly or quite reaching the caudal. 



Plates at side of head connected .... Clarices. C l/i 



Plates at side of head reduced, separated •^ 



by an interspace AUahenchelys, C'arrialabes, 



Gyinnallahes, Chunnalabes. 



Saccobranchus . often placed in a separate group, is pre- 

 cisely similar to Clurias in osteological characters. The 

 plates protecting the sides of the head are present in all the 

 members of the famih^, and I have satisfied myself that 

 Bouleiiger's statement to the contrary for the degraded 

 genera allied to Clarias is erroneous. These plates are 

 present in most Siluroids, but not so strongly developed ; 

 tlie anterior belongs to the circumorbital series, the posterior 

 transmits the lateral line to the prseoperculum. 



Family 14. Pangasiidae. 



The Indian genus Pamjasius differs from the Bagridae 

 externally in the long anal fin, with 28 to 40 rays ; maxillary 

 and one pair of mandibulary barbels are present, but no 

 nasal barbels. The skeleton is very similar to that of 

 generalized Bagridge, difiering only in the development of 

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

 poj)hyses of the fourth 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-clei thrum. The 

 air-bladder consists of an anterior division, corresponding 

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

 Vertebrae 15-1-29. 



Family 15. Synodontidae. -3/ - 



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 ami there is no 

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

 nuchal shield with parallel edges ; the epiotics are small, 

 hidden beneath the supraoccipital ; pterygoid and meso- | 

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



linn. & Mag. N, Hist, Ser, 8, VoL viii. 38 



