794 MR. F. DAY ON THE FISHES OF YARKAND. [Dec. 5, 



partially free in the abdomen, as is seen in genus Boiia. But 

 granting Kessler's description to be accurate, I cannot think tbat 

 such a fact alone would justify instituting a new genus for the recep- 

 tion of his species. 



The reason for air-vessels being enclosed in bone in some fishes is 

 very obscure ; and I sometime since adverted, in the ' Proceedings ' 

 of this Society, to the circumstance of such not being infrequent in 

 Indian Siluridce. 



I found amongst the Indian genera of Siluroids of the fresh 

 waters, or those which entered fresh waters, as follows : — 



A. Air-vessel free in the abdominal cavity. 



1. Rita; 2. Erethistes; 3. Pseudeutropius ; 4. Silurus; 5. Olyra; 

 ft. Macrones ; 7. Callichrous ; 8. Wallago; 9. Arins ; 10. Hemipi- 

 jnelodus*; 11. Osteogeniosus ; 12. Batrachocephalus ; 13. Panga- 

 sius ; 14. Plotosus. Of these, five (no. 9, 10, 11, 12, and 14) are 

 marine forms, entering fresh waters for predaceous purposes. 



B. Air-vessel more or less enclosed in bone. 



1. Ailia; 2. Ailiichthys ; 3. Sisor ; 4. Bagarius; 5. Amblyeeps ; 

 6. Saccobranchus ; 7 • SUnndia ; 8. Eutropiichthys ; 9. Gagata ; 

 10. Pseudecheneis ; 11. Exostoma ; 12. C 'I 'arias ; 13. Glyptoster- 

 num. All of these are freshwater genera. 



Thus the necessity for the air-vessel being enclosed in bone appears 

 to be restricted to the fishes of fresh waters of the plains or hills. 



These thirteen freshwater genera having the air-vessel enclosed in 

 bone are divisible as follows : — 



1. Waters of plains. 



o. Large rivers : no suckers on the chest. Ailia, Ailiichthys, 

 Sisor, Bagarius, Silundia, Eutropiichthys, Gagata. 



/S. Large rivers : descending to the sea. An accessory air- 

 breathing apparatus. Cf arias. 



y. Smaller rivers, tanks, &c. An accessory air-breathing sac. 

 Saccobranchus. 



2. Waters of the plains or hills. 



No sucker on chest. Amblyeeps. 

 Sucker on chest. Gly p tost er num. 



3. Waters of hills. 



Sucker on chest. Pseudecheneis. 

 Chest adhesive. Exostoma. 



* I erroneously gave the air-vessel as enclosed in bone in Hcmipimelodus. 

 The genus was defined by Eleeker ; and it was suggested that Pimelodus cenia, 

 H. B., was an example. Not having an estuary or marine species, as H. jatius, by 

 me, 1 took P. cenia, H. B., as one of the genus ; whereas I now find that it belongs- 

 to Gagata, which embraces P. cenia, P. viridescens, P. itchkeea, and two or three 

 other species. Pimelodus jatius, H. B., has no palatine teeth, as stated in the 

 'Fishes of the Ganges;' it is a Hemipimelodus, Blceker; and of it I possess 

 specimens from the Hooghly ; but I consider such as probably only a variety of 

 Arius. 



