ARTIFICIAL KEY. 27 



pp. Bones of jaws co-ossified, the maxillary with the pre- 

 mazillary, the deatary with the articular. 



Plectognathi, XXII. 



00. Pectoral fins pediculate, the basal bones reduced in number 



and elongate, the gills in their axils. Pediculati, XXIII. 



More than two hundred families are now recognized among the 

 true fishes. The characters on which family divisions are based 

 are usually internal, and often difficult for the beginner to ascer- 

 tain. The boundaries and definitions of many families are also 

 still uncertain. Instead, therefore, of giving a natural analysis 

 under each order of the families included within it, I have thought 

 it best to give instead an Artificial Key by which the student can 

 recognize any of the families of True Fishes included in this work. 

 For analytical keys showing, in some degree, the natural charac- 

 ters, the student is referred to Jordan and Gilbert's Synopsis of the 

 Fishes of North America. A repetition of these analytical tables 

 would consume considerable space, and would not be of much aid 

 to any but advanced students. 



Artificial Key to the Families of True Fishes included in the 

 Present Work. 



Seeies I. Vbntkai, Fins peesent, abdominal. 



A, Dorsal fins two, the anterior rayed, the posterior adipose. 

 B. Body naked ; head with 4 to 8 barbels ; dorsal and pectoral each with 



a strong spine Silceid^ 24. 



BB. Body scaly ; no barbels j no spines. 



C. Maxillary wanting, or grown fast to premaxillary ; head scaly. 



Synodontid^, 32. 

 CC. Maxillaries distinct; head naked. 

 D. Scales ctenoid; margin of upper jaw formed by premaxillaries 



alone PEKCOPSiD.a;, 38. 



DD. Scales cycloid; margin of upper jaw formed in part by maxil- 

 laries. 

 E. Stomach a blind sac, with few pyloric cseca. (Smelt, etc.) 



Akgentinid^, 33. 



EB. Stomach siphonal, with many pyloric cseca. SalmonidjB, 34. 



AA. Dorsal fin single, with free spines before it; body naked, or with bony 



plates ; ventral rays, I, 1, ....... Gasteeosteid^, 45. 



AAA. Dorsal fins two, the anterior of simple rays or spines, the posterior 

 chiefly of soft rays; ventrals, I, 5. 

 F. Teeth very strong, unequal; a lateral line present. SphyejEnid^ 48. 

 FF. Teeth small, subequal; no lateral line. 



G. Dorsal spines slender, 4 to 8; anal spine 1. . Atheuinid^, 47. 



GG. Dorsal spines stout, 4; anal spines, 2 or 3. . . . MoGiLiDiE, 46. 



AAAA. Dorsal fin single, of soft rays only (sometimes preceded by fulcra or 

 followed by finlets). 

 H. Tail evidently heterocercal. (Ganoid fishes.) 

 /. Caudal forked, the lower lobe well developed. 



