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 succeeding vertebræ as far as the ninth caudal. The last ten vertebræ are without processes or neural arches. Sir William Turner states that the caudals of _M. bidens_ are without vertical foramina, but the figure in Van Beneden and Gervais’ Osteography (plate 22) shows them in the same position as in _M. europæus_. The inferior ridges, however, appear to be imperforate in the former species. RIBS.