64 MONOGRAril OF DUE A DEN. 



view of the left half of the dermal skeleton from the inner side, and lies in 

 the same block with a number of Holoptychii. 



The slender-looking fish measures fifteen inches and a half in length, while 

 its depth nowhere exceeds an inch and three quarters, attaining this amount 

 about the middle of the body, and diminishing thence with almost equal rapi- 

 dity towards the head and the tail. The exact length of the head is nowhere 

 precisely determinable, but, from the extremity of the snout to the posterior 

 edge of what seems to be the operculum [h] is a distance of three inches. The 

 depth of the head, including the lower jaw, nowhere exceeds an inch. 



The end of the snout is obtusely pointed, and from it, a bony bar, which 

 may be the remains either of the premaxillary and maxillary bones, or of 

 the ethmoid and sphenoid, is traceable backwards along the line of the base 

 of the skull. A much more slender broken line of bony matter, which attains 

 at most a distance of three-eighths of an inch from the preceding, is all that 

 remains of the roof of the cranium. The matrix fills the interspace between 

 these two thin portions of bone, and exhibits a faint circular impression which 

 may possibly have been produced by the eye. 



Three-eighths of an inch from the end of the snout, the lower bony bound- 

 ary of the skull gives attachment to the enlarged base of a great tooth (a). 

 This base is fully a quarter of an inch in diameter, but the tooth rapidly 

 narrows, so that, although not more than an eighth of an inch of it remains, 

 its broken end is less than an eighth of an inch in diameter. The outer sur- 

 face of the tooth is marked with longitudinal striae. (See the magnified view 

 -4.) Immediately behind this tooth is seen the impression of the pointed 

 apex of another large tooth which must have been implanted in the mandible. 



The exposed ramus of the mandible is either broken at its extremity, or 

 did not extend so far forward as the premaxilla. It is very slender anteriorly, 

 not exceeding one-eighth of an inch in thickness, but, an inch from its an- 

 terior extremity, it rises into a rounded coronary elevation, and attains a depth 

 of one-fourth of an inch. Behind this point it is broken away. 



A confused bony expansion, resulting, to all appearance, partly from the 

 petrosals, and partly from the pre-operculum, lies above the coronary portion of 

 the mandible, while, posteriorly, part of what I take to be the operculum, is seen 

 at b. The surface of this bone exhibits a grooved and ridged sculpturing. 



An indication of a pectoral fin is shown at c, and behind this, the inner 

 faces of the successive rows of rhomboidal scales are exhibited, the anterior 

 series being obscured by the matrix. These scales are thin, smooth internally 

 and, in the middle of the body, about a sixth of an inch wide in their trans- 

 verse or short diameter. 



The outer face of no one of these scales is exhibited, but the casts (B) left 

 upon the surface of the stone whence they have been detached, show that the 

 external surface of each scale was pitted and ridged almost as in Glypto- 

 pomus. The scales are, however, very much thinner and less bony than in 

 that fish. 



The sculpture exhibits a certain tendency to a radiating arrangement, lon- 

 gitudinal strias diverging from the anterior to the posterior margin as is seen 

 in the enlarged scale B. 



