484 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
Gill-arches 4. Pseudobranchiz edie Scales moderate, pronouncedly 
pectinate. 
The genus Silus Gill* was founded upon a misconception. The scales 
of Argentina silus (Cuv.) Nilss., are ‘ dentigerous,” it is true, but not 
ctenoid. They are true cycloid scales, with dentigerous surfaces. The 
diagnosis of Silus Gill would include the form above described, but, as 
has been remarked, it was founded upon a misunderstanding, and oe 
can be no question as to what his intention may have been. 
43. Hyphalonedrus chalybeius, new species. 
DESCRIPTION.—Body plump, terete, its height (16) contained six times 
and one-fourth in its length, its width (15) seven and three-fourths. 
The height at ventrals (16) is equal to that of the origin of dorsal, the 
dorsal being inserted at the highest portion of the body, its middle over 
the origin of the ventrals. The least height of the tail is half that of the 
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 prominent, straight, containing about 52 scales. Between the lateral 
line and the origin of the dorsal are 64 scales, the origin of the ventral 6. 
The greatest length of the head to the end of the flexible flap of the oper- 
culum (27) slightly exceeds one-fourth of the body-length, and is itself 
slightly more than four times the length of the snout (6). 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, and extends back to a perpendicular from the 
anterior margin of the pupil. The articulation of the mandible is in ad- 
vance of the posterior tip of the 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 tip still projects noticeably. 
The dorsal fin is located almost midway between the snout and the 
adipose dorsal. Its height is almost equal (19) to that of the ventral 
(18). The adipose dorsal is over the middle of the anal, its length half 
the diameter of the orbit. 
The distance of the anal from the snont (76) is about three-fourths of 
the body-length. Its length of base (6) is equal to the length of the 
snout; its height (10) to that of the middle caudal rays. The caudal is 
furcate. The pectoral is long, subfalcate, inserted close to the branchial 
cleft, its tip extending to the fourteenth or fifteenth scale of the lateral 
line, its length (22) twice that of the mandible. 
The ventral is located two-fifths of the way from the snout to the base 
of the caudal, and directly under the middle of the dorsal. 
Radial formula: D. 11 + 1 (adipose); A. 8; C.16; P.17 or 18; V.9 
or 10; L. lat. about 52. 
Color grayish mottled with brown, scales metallic silvery. 
ci - *Proc. Acad. Nat. Sci. Phila. 1862, p. 15. 
