NATURAL SCIENCES OP PHILADELPHIA. 101 



XXX. A representative of the Etheostomid family was procured by the TJ. S. 

 and Mexican Boundary Commission, at the mouth of the Rio Grande del Norte 

 (Rio Bravo). It constitutes a new generic type, allied to Cato7iotus, and to 

 which we have applied the name of Alvarius, with the following characters : 

 Head elongated and tapering ; mouth terminal, large, not protractile, lower 

 jaw longer than the upper. Teeth very minute, opercular apparatus, cheeks, 

 and throat scaly. First dorsal fin nearly equal in height to the second, from 

 which it is quite distinct. Anal fin much smaller than the second dorsal ; 

 caudal fin truncated. Five soft rays to the ventrals. Ventral scales uniform. 



As to the species, its body is slender and elongated, the head being subcorn- 

 eal and tapering forwards. The latter enters four times and a half in the total 

 length. The eye is subelliptical ; its horizontal diameter entering about four 

 times in the length of the side of the head ; once in advance of its anterior 

 rim. The posterior extremity of the maxillar bone corresponds to a vertical 

 line drawn in advance of the pupil. The first dorsal fin is subtriangular in its 

 outline ; its base is nearly equal to that of the second dorsal, from which it is- 

 separated by a small space. The anterior margin of the anal is situated some- 

 what behind the origin of the second dorsal ; both fins terminating evenly. The 

 ventrals and the pectorals are rather slender. D vi ; 10; A 8 ; C 5, 1, 6, 6, 1, 6; 

 V 5 ; P 14. The scales are very small, finely pectinated posteriorly ; the lateral 

 line being median. The ground color is light yellowish brown ; the dorsal 

 region being occasionally maculated, and the middle of the flanks provided 

 with a narrow blackish streak which extends along the sides of the head to the 

 apex of the snout. This lateral streak has suggested the appellation of A. 

 lateralis, which we have bestowed upon this species. The fins are unicolor, 

 except the caudal, which is transversally barred, and the first dorsal which ex- 

 hibits a black spot at its upper and posterior edge. The largest specimens ex- 

 amined measure somewhat less than two inches in total length. 



XXXI. A mere glimpse at the " Ichthyologia ohiensis" is sufficient to convince 

 every impartial writer, that Etheostoma blennioides was never intended to typify 

 the genus Etheostoma.* The latter is subdivided into two subgenera : Aplesion, 

 in which the spinous and the soft portions of the dorsal fin are combined ; and 

 Diplesion, in which the same parts are distinctly separated. Now, E. blennioides 

 falls immediately under the head of Diplesion. 



Another species of the genus Diplesion inhabits the waters of Chihuahua 

 river. Specimens of it were collected by Mr. John Potts, of Chihuahua, and 

 sent to the Museum of the Smithsonian Institution. We call it D. fasciatus. 



It has the same general blennioid aspect as its congener: the total length of 

 the specimens observed, measuring about two inches and a quarter, the head 

 entering in it four times and a half. The eye is of medium size, subcircular ; 

 its diameter being contained four times in the length of the side of the head. 

 The first dorsal fin is lower and longer than the second, to which it is con- 

 tiguous. The anal is well developed, rather deeper than the second dorsal, but 

 shorter upon its base. The caudal fin is subtruncated. The ventrals and 

 the pectorals are of moderate development ; their tips being nearly even. The 

 rays are ; D x ; 12 ; A i, 8 ; 6,1,6,6,1,6; V i, 5 ; P 11. The scales are 

 small, deeper than long, posteriorly rounded off and minutely pectinated, whilst 

 their anterior margin is truncated, exhibiting numerous radiating furrows upon 

 the latter section only. Their imbrication takes place after the fashion of the 

 sciaenoids: instead of longitudinal series, they constitute transverse, oblique 

 series. As to the coloration it is but imperfectly preserved. Transverse bands of 

 deep chestnut brown alternate with white or yellowish ones. These bands, or 

 fascia?, are better defined below the lateral line than above it, where they are 

 sometimes interrupted. The head is brown, with a vertical black streak across 



* Amer. Journ. of Sci. and Arts. Second series, xvii. 1854, 305. 

 1859.] 8 



