Fig. 27. Skeleton of Amphibamus grandiceps Cope. × 1.4.
c, carpus; cl, clavicle; cr, caudal rib; cv, caudal vertebra; f, femur; h, humerus: il, ilium; s, skin: or, orbit: r, radius; ul, ulna; sc, scapula; sp, sclerotic plates; t, tibia and fibula; ts, tarsus; vs, ventral scutellæ. Specimen No. 794, Yale University Museum.
One of the most interesting features of the Yale specimen is the preservation of a small patch of skin, evidently from the back, lying to one side near the head, measuring 5 mm. in length by 3 mm. in width. The fragment shows the skin to be of tuberculated scales, 4 of which occupy the length of 1 mm. The scales are somewhat hexagonal, almost rounded, and were relatively quite thick. They lie in a close mosaic ([fig. 27]).
The Yale specimen has, very well preserved, a portion of the ventral scutellæ, of the throat, chest, and belly. The arrangement of the plates on the throat and chest is almost exactly the reverse of what Credner has described ([190]) for Branchiosaurus amblystomus Cred. On the throat, in the present form, the chevron points anteriorly, and it is the anterior prolongation of the belly scutes with the postero-lateral projection of the gular scutes which form the chest and arm scutellation. The belly chevrons point anteriorly, as in Branchiosaurus, the rods formed by the scutes being straight and not curved as in Branchiosaurus. The entire ventral armature preserved is displaced to the left of the animal and only the anterior portion is preserved.
The pectoral girdle is only partially known. The scapula is crescent-shaped. The other elements are indicated only by fragments and nothing is known of their form.
The arm elements are nearly all known. The humerus is slender and expanded at the ends, with its articular surfaces well developed. The separate radius and ulna are of approximately the same size and length. The carpus is unossified. The complete phalangeal formula for the hand of Amphibamus is unknown. The third digit seems to have 4 elements. The formula 2-2-3-2 has been suggested ([462]).
The pelvis is very satisfactorily known. The ilium is a long, slender, straight rod, with expanded ends. The ischium is shown on both sides of the vertebral column in the Yale specimen. Its form is almost identical with that of Paleohatteria longicaudata Credner, from the Rothliegenden of Saxony. The ischia are apparently approximate in the median line, though this character is somewhat obscured by the impression of the caudal vertebræ. Their relation with the ilium, other than that they were posterior to it, is uncertain. The pubis is, apparently, calcified cartilage. It is a squarish plate, somewhat corrugated, lying anterior to the ilium in the Daniels specimen. The elements of the pelvis were undoubtedly hung loosely in the flesh, as in modern salamanders, since there is no indication of articular surfaces.
The hind limb is well known, the type having a nearly complete leg with the foot. The Daniels and the Yale specimens supplement and substantiate the type. The femur is longer than the humerus, but more slender, with its articular surfaces about as well developed as in the humerus. The element is a simple rod of bone without muscular crests of any kind. The tibia and fibula are, likewise, slender separate rods of bone. The tarsus is unossified. The phalangeal formula is 2-2-3-4-3, and is fairly definite.