Chapter M

Length of centrum ·010
Breadth of centrum ·040
Depth of centrum ·027

As Professor Marsh has given no measurements, the reference to _A. depressa_ cannot be certain.

The specimen was found at Henry's Fork.

Amia scutata, Cope.

Bull, of U. S. Geol. Survey, No. 1 of Series II, p

A species of about the size of _A. calva_, but with a proportionately larger head. It is represented in our collection by a specimen which lacks only a portion of the caudal and pectoral fins. The _premaxillary_ is short and stout, articulates closely with the maxillary, and bears a single row of pointed recurved teeth. These are shorter and straighter than in _A. calva_. The _maxillary_ is much as in the modern species, but is rounder. The cranio-facial axis is straight and broad; the _basioccipital_ is the largest of the bones; the _basisphenoid_ and _presphenoid_ are of the usual shape and size, but there is a constriction at their junction which is not marked in the modern species. The _vomer_ is long and double, and at the extremity is armed with rows of small teeth. The two portions diverge more perceptibly than in _A. calva_, and are stouter, though this appearance may, to some extent, be due to flattening.

The _frontal_ is long, broad, and thick; the upper surface is delicately sculptured in a somewhat different pattern from that seen in the modern species. The _parietal_ is short and broad, while the _epiotic_ is unusually narrow. The _mandible_ is long and slender; the rami are incurved anteriorly, but apparently not to the same extent as in _A. calva_. The articular has the shape of a long and narrow wedge; it does not form a very close articulation with the dentary. The dentary is long and comparatively slender, has a rounded outline, and is occupied by an external row of large, and an internal band of small teeth. The mandibular teeth, like those of the upper jaw, are somewhat different from the teeth of _A. calva_; they are shorter, stouter, and are not so much incurved or recurved. They are very sharp, and show a constriction below the apex. The small teeth are of the usual size and shape. The jugular plate is well developed, and is long and narrow. The _hyoid arch_ is very much the same as that shown in the recent species; the characteristic flat branchiostegals are well marked; they appear to be thirteen in number.

The _scapular arch_ is long and stout. The _clavicle_ is strongly bent, the supra-clavicle is short, and the _post-clavicle_ is long. The pectoral fin is too indistinct for description.

The _vertebræ_ are of considerable depth in the anterior dorsal region, and decrease steadily in size as they go backwards. The neural spines are long and slender, and project strongly backwards. The relation of the centra to the arches seems to be about that seen in _A. calva_, but the neurapophyses are more slender. The diapophyses are long and slender, in this respect differing from the Bridger species and approaching the modern one. The dorsals are thirty-five in number. The caudals number about forty-seven. They have smaller centra, but longer and stronger neurapophyses than the dorsals. The hæmal arch is long, and the hæmapophyses articulate movably with the centra. The spines supporting the caudal fin rays are very stout. The dorsal fin is long and soft, and has long interneurals supporting short rays; these are fifty-three in number. The anal fin, on the other hand, is very short, having but nine rays, which are long and jointed, and articulate with short interhæmals. The caudal fin appears to be of the usual form. The _femur_ is of the general shape characteristic of _Amia_, but is not just like that of _A. calva_. It is shorter, broader at the proximal end, while the distal end is narrower, and has a deeper constriction just above it. The ventral fins are placed under the middle of the dorsal region, and have each ten rays. The scales are of the usual cycloidal shape, and minutely striate.

_Measurements._