1856.] 201 



10. MoNiANA coucHi, resembles M. gracilis most ; is, however, distinguished 

 from it by a less fusiform body and a much shorter head. This feature may be 

 traced upon series of specimens of both species with an unfailing constancy. 

 The eye is smaller also, and so is the mouth as might be deduced from the cha- 

 racters just alluded to. 



From the vicinity of China, New Leon, Mexico ; collected by Lieut. Couch, 

 U. S. A. 



11. MosiANA RUTiLA, has the general physiognomy of M. gracilis, from which it 

 differs by a more advanced position of the dorsal fin and larger scales. Dorsal 

 region greyish ; sides and abdomen golden. 



From Cadereita, New Leon, Mex. ; collected by Lieiit. D. N. Couch, U. S. A. 



12. MoNiANA NiTiDA. This spBcies differs from JI.eouchi by a more elongated 

 and fusiform body, more elongated head and much larger eye. From M. rutila 

 it differs by the same characters of the body, but the head differs by the flatten- 

 ing of its upper surface. There are eleven longitudinal rows of scales upon the 

 line of greatest depth of the body, five above and five below the lateral line. 

 The latter, therefore, is nearly medial, forming but a slight curve upon the 

 middle of the abdomen. Color pale red, sides of head and middle of the flanks 

 silvery. 



Collected at Cadereita, New Leon, by Lieut. D. N. Couch, U. S. A. 



13. Montana Formosa. The prettiest species of the genus ; the body is ellipsoid 

 in profile and the tail very much tapering. The region above the lateral line is 

 blackish brown in the adult, and reddish brown in the young, occasionally also 

 dotted with black ; the inferior regions are reddish yellow anteriorly and yel- 

 lowish red posteriorly. 



Numerous specimens of this species were collected in the Eio Mimbres, Mex. 



14. MoNiANA GRACILIS. A Very graceful and slender species, resembling most 

 J/, lulrensis, from which it however differs by a much smaller head and a more 

 arched back ; the body itself is more compact. Ash grey above, yellowish white 

 beneath ; flanks silvery. 



Specimens were collected near Monterey, New Leon, by Lieut. Couch, U. S. A. 



15. Montana gibbosa. May readily be distinguished from all its congeners by 

 a short and arched body, resembling a cyprinodon as much as any fish we might 

 compare it to. Pale reddish above, whitish beneath ; sides silvery. 



Specimens collected ai Brownsville, Texas, by Capt. Van Vliet, U. S. A. 



16. MoNiANA TRisTis. A slender and graceful species, subfusiform in profile, 

 though the back is rather arched. The peduncle of the tail is long and of 

 nearly uniform depth. The head constitutes about the fifth of the length. Eleven 

 rows of scales, five above, five below the lateral line. Reddish brown. 



Brought home by Lieut. E. G. Beckwith, U. S. A. 



The " Fauna Boreali Americana " records under the name of Cyprinus (Abra- 

 nis,) baltcaius, a species of this family, which bears a strong external resemblance 

 to the large species of Luxilus, and so much so, that, on a superficial examina- 

 tion, no one would hesitate to refer it to the latter genus. The structure of the 

 pharyngeal teeth affords the most striking generic differences, as will be seen 

 further on. In selecting for it the name of 



RICHARDSONIUS, 



we have borne in mind the eminent labors of the author of the work just referred 

 to. We will characterize the genus by saying, that the body is very compressed, 

 subelliptical or fusiform in its outline and deep upon its middle. The head is 

 proportionally small ; the mouth terminal, slightly oblique, constructed as in 

 Luxilus, but somewhat larger, yet unprovided with cirrhi or barbels. The eye 

 is large. Isthmus very narrow. Caudal fin forked ; insertion of ventrals situ- 

 ated in advance of the anterior margin of the dorsal. Anal fin longer than the 



