484 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Gill-arches 4. Pseudobranchiae present. Scales moderate, pronouncedly 

 pectinate. 



The genus Silun Gill* was founded upon a niisconception. The scales 

 of Argentina silus (Cuv.) Nilss., are " denti.^erous," it is true, but not 

 ctenoid. They arc true cycloid scales, with dcntigorous surfaces. The 

 diagnosis of iSilx.s Gill would include the form above described, but, as 

 has been remarked, it was founded upon a misunderstanding, and there 

 can be no question as to what his intention may have been. 



43. Hyphalonedrus chalybems, new species. 



Description. — Body plump, terete, its height (10) contained six times 

 and one-fourth in its length, its width (l.">) seven and tliree-fonrths. 

 The height at ventrals (10) is equal to that of the origin of dorsal, the 

 dorsal being inserted at the highest portion of the body, its middU', over 

 the origin of tl>e ventrals. The least height of the tail is half that of tlie 

 body. The scales are moderately strong, and sharply' pectinated at the 

 edge, and arranged in regular transverse rows, overlapping in such a 

 manner as to resemble oblique plates upon the sides. The lateral line 

 is ])romineut, straight, containing about 52 scales. Between the lateral 

 line and the origin of the dorsal are Gh scales, tlie origin of the ventral G. 

 Tlie greatest length of the head to the end of the flexible flap of the oper- 

 culum {21) slightly exceeds one-fourth of the body-length, and is itself 

 slightly more than four times the length of the snout (0). The longi- 

 tudinal diameter of the orbit (8) is four times that of the interorbital 

 space (2). The maxillary, broad and flattened posteriorly, is in length 

 (10) one-tenth of the body, ami extends back to a perpendicidar from the 

 anterior margin of the pupil. The articulation of the mandible is in ad- 

 vance of the posterior tij) of 1 he maxillary, its length (11) slightly greater, 

 and it protrudes beyond the snout, when the mouth is open, a distance 

 greater than the width of the interorbital area. When the mouth is 

 closed its ti}) still projects noticeably. 



The dorsal tin is located almost midway between the snout and the 

 adipose dorsal. Its height i<s almost equal (19) to that of the ventral 

 (18). The a<li])0se dorsal is over the middle of the anal, its length half 

 the diameter of the orbit. 



The distance of the anal from 'the snout (70) is about three-fourths of 

 the body-length. Its length of base (0) is equal to the length of tlie 

 snout; its height (10) to that of the middle cauchil rays. The caudal is 

 furcate. The jjectoral is long, subfah^ate, inserted clos<>. to the branchial 

 cleft, its tip extending to the fourteenth or tifteenth scale of the lateral 

 line, its length (22) twice that of the mandible. 



The ^'entral is located two-tifths of the way from, the snout to the base 

 of the caudal, and directly under the middle of the dorsal. 



Eadial formula: D. 11 + 1 (adipose); A. 8; C. 10; P. 17 or 18; V. 

 or 10 ; L. hit. al5out 52. 



Color grayish mottled with brown, scales metallic silvery. 

 *Proc. Acad. Nat. Sci. Phila. 1862, p. 15. 



