with the basioccipital. These elements are smaller than the homologous parts of B. marshi and B. discus and are hardly more than half the size of B. robustus. They differ in several minor characteristics. The atlas resembles B. marshi and B. robustus in having a single hypapophysis on the lower anterior surface of the centrum. The third and fourth cervicals differ from the same elements of B. marshi in having well developed parapophyses, and very small diapophyses.
There is no indication of the parapophysis on the axis as found in both B. marshi and B. discus. Just below the diapophysis and separated from it by a non-articular tract is a faint antero-posterior ridge, which anteriorly probably represents
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| Fig. 6. Atlas, axis, third, and fourth cervical vertebræ of Baptanodon natans (No. 1441). One half natural size. 1. Coalesced atlas and axis. 2 and 3. Third and fourth cervicals. d., diapophysis; p., parapophysis; z., hypapophysis. | Fig. 7. Lateral view of intervertebral disk of Baptanodon (No. 1441). One half natural size. |
the rudimentary parapophysis of the atlas. Midway between this ridge and the lower border is a small vertical eminence not observed in the other species. The upper arches of these vertebræ are not sufficiently well preserved to be described here. The other vertebræ preserved appear very similar to the corresponding elements in the other members of this group.
Intervertebral Disks.— Fig. 7 represents the shape and size of the matrix filling the space between the centra of the anterior vertebræ. These biconvex disks are quite uniform in character and give an accurate idea of the thickness of the cartilage that once filled the spaces between the centra. The average thickness of the disks at their middle is about 30 mm.
Anterior Limbs.— About half of the proximal portion of one humerus was found. Fig. 8 shows the subrectangular outline of this articular end. The surface of this
