NATURAL SCIENCES OP PHILADELPHIA. 491 



Form. The body is triquetrous in front, declining from the dorsal ridge to 

 the sides of the plane abdomen. The greatest height equals an eighth ( - 12) of 

 the total length from the snout to the vertical from the end of the caudal fin. 

 The greatest breadth is a fourth greater (= -15) than the height. Behind the 

 anus and ventral fins the tail becomes abruptly slender and compressed, the 

 height entering fourteen times (= -07) in the length and about twice as high 

 as at the base of the caudal (= 03|). The back in front of the dorsal gently 

 declines and meets the forehead, from which it is separated by a slight groove, 

 and is itself furrowed in the middle. 



Head. The head from the snout to the branchial region forms more than a 

 sixth ( - I7i) of the length. The height at the forehead equals -10J, and at the 

 margin of the superciliary ridge a ninth ( - 11) of the total length. The width 

 between the external margins of the superciliary ridge nearly equals a twelfth 

 (08) of the same length, and the greatest width at the cheeks is nearly twice 

 as great (= -15). The forehead or interorbital area is nearly plane between 

 the superciliary ridges or scarcely convex along the middle. The superciliary 

 ridges are blunt, very hard, angulated and obliquely truncated behind, and 

 incurved inwards ; they merge into the widening but less conspicuous ridges 

 in front, which are continued to the snout, where they are separated by a shal- 

 low furrow and a slight depression; the rest of the profile is channelled. The 

 cheeks are very tumid. 



Eyes. The eyes are oval ; the longitudinal diameter between the skin about 

 equals a sixth (-03) of the head's length, and that of the outer ring a fourth 

 (04J). The distance from the snout equals a half (-09) of the head's length. 



Mouth. The mouth is transverse, the margin of the lower jaw describing the 

 three sides of a nearly regular octagon, and the distance from one corner to the 

 other equals a twelfth (-08) of the total length, and four-fifths of the width 

 of the head at the same vertical. The patch of teeth encroaching on the out- 

 side of that jaw is transversely fusiform. 



Teeth in front of each jaw digitated, with a median cusp and two on each 

 side, which become lateral and directed outwards on teeth next to the symphy- 

 sis ; they are arranged in five rather oblique rows, each row in the upper jaw 

 having six on each side of the symphyseal ones, and in the lower, four. The 

 area with molar teeth equals in length the width between the lower lips. 



Fins. Tbe first dorsal originates at the vertical from the beginning of the 

 last third of the base of the pectoral fin, or near the front of tbe second fourth 

 of the total length (27 J). Its attached base nearly equals a twelfth ( - 08) of the 

 same length, and the free-extension backwards to the posterior angle a sixteenth 

 (06). The spine is rectilinear, rather exceeds a tenth of the length, and its 

 compressed base forms half of the base of the fin itself. The margin of the 

 fin describes a parabolic curve backwards to the " anterior angle," which is 

 obliquely rounded and projects rather farther backwards than the "posterior 

 angle;" the latter is little acute, and the margin between it and the anterior is 

 vertical and little emarginated. The greatest (oblique) height rather exceeds 

 an eighth (-13) of the total length. 



The second dorsal is similar in form to the first, but less elevated in propor- 

 tion, and with the anterior angle not extending beyond the posterior, and the 

 emargination deeper. The distance from the snout exceeds a half ( - 54) of the 

 total length, and that from the posterior angle of the first dorsal equals the 

 base of that fin to such angle. Its base equals about a fourteenth (07J) of 

 the length, and the posterior angle extends nearly a nineteenth (-05^) more 

 behind. The spine is rather more oblique than that of the first dorsal; its 

 base forms two-thirds of that of the entire fin, and its length equals a tenth of 

 the total. The greatest (oblique) height of the fin equals a ninth (-11) of the 

 total length. 



The anal fin commences at the middle between the sixth and seventh-tenths 

 (65) of the length, or rather in advance of the posterior angle of the second 



1862.] 



