NATURAL SCIENCES OP PHILADELPHIA. 265 



D. 12, 28. A. 2, 32. C. I. 1, 8, 1, I. P. 13. V. 3. 



The color appears originally to have been nearly uniform and whitish blue 

 or almost white on the trunk ; when the scales are lost the apparent color is 

 grayish, marbled or spotted with white. The head is whitish or grayish 

 above, variegated with coarse meandering darker lines, which partly also ex- 

 tend on the suborbital region and cheeks. The preoperculum, and other 

 opercular bones are mostly immaculate. The fins are also immaculate. 



The body is slender and very gradually and with much regularity declines 

 towards the caudal fin ; it is also much compressed, especially posteriorly. 

 The height is greatest at the front of the dorsal fin, and is there nearly equal 

 to a seventh (14-100) of the total length. The height behind the last dorsal 

 ray exceeds little more than a fourth of the greatest, and only equals a twenty- 

 fifth part (4-100) of the length. The thickness at the bases of the pectoral 

 fins is contained twelve times (8-100) in the length. 



The head is plane above and angulated at the sides of its superior surface. 

 From the tip of the closed lower jaw to the margin of the bony operculum it 

 constitutes nearly a fifth (19-100) of the extreme length. Its height between 

 the crown and the inferior margin of the preoperculum is much less than two- 

 thirds of its length (11-100 of the total). The height at the articulation of 

 lower jaw nearly equals a half of the length (9-100 of the total). The thick- 

 ness of the head is greatest close behind the preoperculum, and exceeds a half 

 of the length, or one-tenth (10-100) of the total ; it thence gradually dimin- 

 ishes to the obtuse snout ; behind the eyes, it equals seven-tenths of the great- 

 est width, or 7-100 of the total length. 



The eyes are moderate, circular and entirely superior. The diameter of 

 the orbit is contained more than six times in the head's length, and equals 

 3-100 of the total length. The distance between the eyes equals two-thirds 

 of the diameter, and the distance from the symphisis of the intermaxillaries a 

 diameter. 



The posterior border of the basal ridge of the preoperculum is nearly ver- 

 tical, and descends toward the angle, which is rounded. The width of the 

 preoperculum is greatest at the angle between the ridge and the free margin ; 

 it is there a half greater than the diameter of the eye (4^-100 of the total 

 length). Near the free margin of the preoperculum, there is a band of paired 

 pores. 



The dentary on its posterior part has three broad transverse channels. The 

 opercular fringe is composed of about fifteen distinct and free filaments. 



The dorsal fin commences at 18-100 of the length from the upper jaw, and 

 has forty or forty-one rays ; about twelve of these are simple and inarticulated, 

 while the others are articulated, and divided on each side of the mesial line 

 to the base, but so connected as to appear like simply articulated rays, especi- 

 ally from a lateral view. 



The anal fin commences under the sixth or seventh ray of the dorsal ; it 

 has about thirty-four rays ; the first two are simple and inarticulated ; the 

 rest are divided to their bases and articulated. 



The caudal fin is narrow, rather long, truncated behind, and furnished with 

 eight branched rays, two articulated and two simple ones. The fin forms 

 nearly an eighth (12-100) of the total length. 



The pectoral fins are acutely angulated ; the superior rays rapidly increase 

 towards the fifth, which is longest, and equals the sixth (16-100) of the total 

 length ; the rays beneath rapidly decrease, and the margin of the fin con- 

 verges toward the base, which extends very obliquely forward. 



The ventral fins are each composed of three articuiated and stout rays, but 

 which are attenuated at the extremities. The external ray is shortest ; the 

 median is little longer than the internal, and equals an eighth (12-100) of the 

 total length. 



The scales are of moderate size and regularly imbricated. The lateral line 

 1861.] 



