18 



arterial bulb is thin and not contractile, and has a pair of oppo- 

 site valves. The intestine is without a spiral valve. The 

 optic nerves cross. 



The proper division of the Teleosts into orders is still not a 

 thoroughly settled question and I will not enter upon special 

 descriptions of them. 1 



Group Physostomi. 



In this large group the air bladder is connected with the 

 alimentary canal by a duct. The fins, with the exception of 

 occasional strong spines in some families, are always soft- 

 rayed. 



Family Siluridae. 

 Catfishks. 



In this family the subopercle is wanting, the anterior verte- 

 brae are grown together, the maxillary is rudimentary and 

 forms the base of the largest barbel, the skin is naked or cov- 

 ered with plates ; there are usually two dorsals, the first with 

 a strong spine, the second adipose. Bach pectoral also has a 

 strong spine. The numerous teeth are in villiform bands. 

 The air bladder is large, generally present, and connected with 

 the auditory ossicles ; it is sometimes partly surrounded by 

 osseous plates. 



^Explanation of abbreviations used in this paper. 



D. — Dorsal fin. 



2d D. — Second Dorsal fin. 



P. — Pectoral fins. 



V. — Ventral fins. 



A. — Anal fins. 



C— Caudal fin (tail). 



Roman numerals used in connection with fins, mean spines or 

 inarticulate rays. 



Arabic numerals indicate soft rays. For example D. XI, 10 means 

 one dorsal fin with 11 spines and 10 soft rays. 



D. X-I, 32 means first dorsal fin with 10 spines, second dorsal fin with 

 1 spine and 32 soft rays. The dash between the numerals indicates that 

 there are two fins. 



Scales 6-42-12 means 6 scales counted vertically from the front of 

 dorsal to the lateral line ; 42 scales in the lateral line itself (if present) 

 or along a side line from head to tail ; and 12 scales vertically from the 

 lateral line to the anus. When only one numeral is given, the number 

 of scales along the side is meant. 



Scutes are the tooth-like scales forming the saw-like margin of the 

 belly in some fishes. 



