class="r">302

Breadth at anteorbital notches 210 205 ^f182 Breadth of beak at middle 66 ... 60 Depth of beak at middle 54 ... 40 Greatest breadth of premaxillæ proximally 168 147 142 The same, in front of anterior nares 111 99 104 Breadth of anterior nares 51 45 42 Length of temporal fossæ 102 115 101 Breadth between temporal fossæ 228 212 208 Breadth of foramen magnum 42 34 34 Length of mandible 654 ... 565 Length of symphysis 135 ... 116 Greatest depth of mandible 120 ... 101

^a Dimensions taken from Van Beneden and Gervais’ figures.

^b Beak lacking. Length from occipital condyles to base of beak (straight), 312 mm.

^c Pterygoids broken.

^d At middle.

^e Estimated. One zygoma is broken.

^f Least.

VERTEBRÆ.

The vertebral formula of three specimens of M. bidens and of the Atlantic City specimen of M. europæus is as follows:

M. europæus.
Atlantic City	C. 7;	Th. 9;	L. 11;	Ca. 20=47
M. bidens.
Landenæs	7;	10;	11;	19=47
Fæø	7;	9;	11;	19=46
Udsire	7;	10;	9;	20=46

Although the skeleton of M. europæus appears from the foregoing formula to include one less thoracic vertebra than those of M. bidens, as the last pair of ribs present is as long as the preceding ones, an additional pair probably existed originally. The formula for europæus would then be: C. 7, Th. 10, L. 10, Ca. 20 = 47. (Pl. 13, fig. 1.)

In the Atlantic City specimen all the epiphyses are free. The atlas and axis are anchylosed together, the third cervical is united to the axis by the centrum, and on the right side by the top of the neural arch; on the left side the arch is imperfect and free. The fourth to the seventh cervicals, inclusive, are all free. The arch is incomplete above in the fourth, fifth, and sixth, but complete in the seventh. There is a short neural spine on both sixth and seventh cervicals. The atlas has a broad, obliquely-truncated inferior lateral process, but no superior process, while the axis has both inferior and superior processes. The inferior process is twice as long as the superior process, and both are directed backward. They do not meet to form a ring. The third to the sixth cervicals, inclusive, have inferior processes only, that on the third being long and thin (but developed on the left side only). On the fourth and fifth cervicals the processes are short and small; on the sixth, long and broad, and directed downward. The centrum of the seventh cervical has a broad facet on the side, where the first rib is attached, and an inferior lateral process thicker than that of the sixth cervical, but also directed downward.

It is doubtful whether the foregoing characters of the cervical vertebræ are of any systematic importance, as there is a very large amount of individual variation among these animals in the development of the transverse processes and other details of structure. M. bidens, however, appears to have superior transverse processes on most of the cervicals which sometimes unite with the inferior processes to form foramina. In the specimen of M. europæus under consideration there are no superior processes, except on the axis.

Metapophyses are first distinguishable on the diapophyses of the fourth thoracic vertebra, and on the seventh assume the form of conical tubercles. On the eighth and following vertebræ they are flat, and are last distinguishable on the seventh caudal vertebra. Facets for the articulation of the tubercles of the ribs occur on the diapophyses of the first to the seventh thoracic vertebræ. On the latter vertebra the first transverse process appears as a short projection on the side of the centrum. On the eighth thoracic vertebra, the transverse process is broad and flat, with the anterior margin bent upward, and is about 48 mm. long. The base of the neural arch is strongly concave externally. The transverse process of the ninth thoracic vertebra is similar to the preceding one, but broader and not bent upward anteriorly. The base of the neural arch is also concave in this vertebra. The ends of the transverse processes of the eighth and ninth vertebræ are emarginate for the articulation of the ribs. A median inferior ridge is first distinguishable on the seventh thoracic vertebra.

As far as can be learned from the descriptions of Turner, Grieg, and others, the thoracic vertebræ of europæus do not present any marked differences from those of bidens.

The transverse processes of the lumbar vertebræ are short, broad, and flat, and somewhat curved forward. They are expanded and rounded at the free ends. The centra increase in length posteriorly, the last lumbar having the greatest length of any vertebra in the column. The neural spines increase in length from the first lumbar to the fourth, those on the remaining lumbars being subequal, but the spine on the ninth lumbar is a little longer than the others. Median inferior ridges occur on all the lumbars and are strongest at the middle of the series. The height of the centrum of the ninth lumbar is 63 mm., width 73, and length 116. The highest neural spine is 233.

As above mentioned, the first of the vertebræ counted among the lumbars may be the last thoracic vertebra, but as there is no indication of an articular facet at the end of the transverse process it is not so considered in this place.

The lumbar vertebræ in M. bidens appears to be more nearly equal in length than in the present species, but are not different otherwise.

The spines of the caudal vertebræ decrease rapidly in height posteriorly, and disappear after the tenth caudal. The transverse processes resemble those of the lumbars, but are shorter. They are last distinguishable on the eighth caudal. The transverse process of the seventh caudal is perforated by a vertical foramen. Similar but much smaller foramina occur on the sides of the centra of the eighth and ninth caudals. In these vertebræ the inferior ridges are also pierced by foramina. In the fourth caudal a ridge appears on the side of the neural arch on a level with the top of the centrum, and similar ridges are found on the