bladder generally present, communicating with the 

 organ of hearing by means of the auditory ossicles. 

 Adipose fin present or absent. 



Inhabitants of the fresh waters of all the temperate and tropical 

 regions, some entering the salt water, but keeping near the coast. 



We give first a synopsis of the Groups, and then one of the Genera. 



Synopsis of the Groups. 



First Subfamily. SILURID^ HOMALOPTER^. 



The dorsal and anal fins are very long, nearly equal in extent to 

 the corresponding parts of the vertebral column. 



Group A. The gill -membranes are not confluent with the skin of 

 the isthmus, remaining separate to the chin. The dorsal is uni- 

 formly composed of feeble rays, or its posterior portion is modified 

 into an adipose fin Clariina, p. 13. 



Group B. The gill-membranes are not confluent with the sldn of 

 the isthmus, or united with it by a narrow strip only, remaining 

 more or less separate. The dorsal is divided into two portions : 

 a short anterior with a strong spine, and a long posterior which, 

 like the anal, is confluent with the caudal. Ventrals many- 

 rayed Plotosina, p. 23. 



Group G. The gill-membranes are confluent with the skin of the 

 broad isthmus, the gill-openings being thereby reduced in extent. 

 The dorsal and anal are divided into two portions : the anterior 

 of the former fin with a strong sjnne, whilst the posterior of both 

 fins are united with the caudal. Ventrals six-rayed. 



Chacina, p. 29. 



Second Subfamily. 



SILURID^ HETEROPTERiE. 



The rayed dorsal fin is very little developed, and if it is present, 

 it belongs to the abdominal portion of the vertebral column ; the 

 adipose fin is exceedingly small or absent. The extent of the anal 

 is not much inferior to that of the caudal vertebral column. The 

 gill-membranes overlap the isthmus, remaining more or less sepa- 

 rate. 



Group D. Ventral fins below or behind the dorsal. The abdominal 

 portion of the vertebral column is much shorter than the caudal, 

 and the anterior vertebrae are confluent into one of large size. 



Silurina, p. 30. 



