74 UNITED STATES AND MEXICAN BOUNDARY. 



and sideways by the maxillar bones. The dentition varies greatly according to the genera ; the 

 teeth may even be wanting. The pharyngeal bones do not exhibit those large teeth which we 

 have observed amongst Cyprinoids. The air-bladder is divided into an anterior and a posterior 

 partition, as is the case in the Cyprinoids, and there is, in addition, a connecting chain of small 

 bones between the same air-bladder and the organ of audition such as may be observed in both 

 Cyprinoid and Siluroid families. The pseudobranchia are not visibly developed, an organic 

 trait by which these fishes may easily be distinguished from the Salmonidae. In such as are 

 provided with an adipose finlet, an oviduct leads the eggs out, not allowing them to fall 

 into the abdominal cavity. The intestine is provided with numerous cceca. 



ASTYANAX, B . & G . 



Gen. Char. — Body compressed ; abdomen not serrated. Scales large. Adipose fin present A double row of teeth on the 

 premaxillaries and anterior portion of the maxillaries. Neither canine nor palatine teeth. Gill apertures continuous under 



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the throat ; branchinstegal rays three on either side. Pharyngeal teeth absent, else so minute as not to be perceptible. Dorsal 

 fin situated above the ventrals. 



Syn.-- Astyanax, B. & G. in Proc. Acad. Nat. Sc. Philad. VII, 1854, 26. % 



The premaxillar teeth have the same structure as those on the lower jaw : Plate VIII, fig. 6, 

 giving a very good idea of what that structure is. The teeth observed at the upper portion of 

 the anterior edge of the maxillar bones are very small, simple, conical, imperceptible to the 

 naked eye. 



The species described below, the only one so far known of its genus, is the northernmost 



IT 



North America. 



ASTYANAX ARGENTATUS, B . & «• . 



Plate VIII, Figs. 5—9. 



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Spec. Char. — Body rather short, deep, and very much compressed, the head forming about the fifth of the total length. The 

 snout is abbreviated and rounded off; the mouth of medium size, its angles not extending so far back as a vertical line drawn in 

 advance of the pupil. The eye is large and circular ; its diameter entering about three times and a half in the length of the 

 side of the head. Opercular apparatus quite narrow. Dorsal fin higher than long, somewhat concave upon its upper margin ; 

 its anterior edge being placed midway between the extremity of the snout and the insertion of the caudal fin. Adipose fin 

 quite slender, situated opposite the posterior portion of the anal. Caudal fin deeply furcated and longer than the head. Anal fin 

 longer than deep, exteriorly concave, much deeper anteriorly than posteriorly, and inserted backwards of the dorsal. The 

 ventrals, rather slender, are inserted nearly under the middle of the dorsal The pectorals, larger than the ventrals, are 

 also slender ; their tips, however, do not reach the insertion of the ventrals when stretched in that direction. 



Syn.— Astyanax argentatas, B. & G. in Proc. Acad. Nat. Sc. Philad. VII, 1854, 27. 



■ 



The scales are deeper than long, somewhat truncated anteriorly. There are no radiating 

 furrows, but some very well marked stria may be observed upon their posterior section. The 

 lateral line is very conspicuous, and slightly bent downwards upon the middle of the abdomen. 



Br. Ill : 111 ; D 1, 10 ; A 1, 21 j C 5, 1, 9, 8, 1, 4 ; V8; P 13. 



The dorsal region is of a deep reddish brown, whilst the sides of the abdomen are of a bright 

 silvery hue ; the fins being reddish yellow. An elongated black spot exists at the base of the 

 caudal fin, extending along the central rays to near the posterior edge of that fin. 



Plate VIII, fig. 5, represents Astyanax argentaius, size of life. Fig. 6 is an enlarged view 

 of the open mouth, in order to show the peculiar shape of the teeth, some of which being 



