The centra of those caudal vertebrae which have chevrons do not differ much in shape. They become less constricted, and, back of the middle of the series, are smoothly cylindrical in shape. The transverse processes decrease gradually in length, disappearing entirely in the twenty-fifth or twenty-sixth. The spinous processes are more or less incompletely preserved in the anterior vertebrae. They increase only gradually in length for the first twenty of the series, and are markedly oblique, with the posterior border stout, and the anterior border alate. With the twenty-sixth they begin to increase more rapidly in length, and have become more nearly vertical in position, and are thinner at each margin. In the thirty-fifth or thirty-sixth they attain their greatest length, and are here directed slightly forwards. Thence to the end of the tail, the length decreases gradually, and, in position, they are directed more and more obliquely backward. The chevrons are strongly oblique throughout the series and are firmly co-ossified with the centrum. The tail, it is thus seen, has a broad, vertical, fin-like extremity, which, doubtless, aided much in the propulsion of the animal through the water. There are sixty-seven vertebrae with chevrons present in the specimen, all continuous, except in one place. The last one is less than one-fourth of an inch in diameter, and shows that there had been yet another, possibly several more. Toward the base of the series the tail has been bent forwards over the back, and it is possible that, where the break occurs, there has been a vertebra lost. The measurements, however, do not seem to indicate any loss. The entire series of vertebrae was not less than sixty-eight, and probably not more than seventy, making for the entire vertebral series one hundred and seventeen to twenty. MEASUREMENTS OF THE CHEVRON-BEARING CAUDAL VERTEBRAE.