224 DR. J. MURIE ON THE ANATOMY [Feb. 14, 
first one, and it makes a long sweeping curve which terminates in a 
tapering manner, truncated, however, at the very extremity ; the 
lower portion is twisted forwards from the general plane of the rib. 
The second rib, unlike the first, appears to be pretty constant in 
shape in different individuals. 
Fig. 4. Heads of the first four ribs. 
The outlines of the heads of the first and second ribs of Benedenia 
knoxit, figured by Dr. Gray (P. Z. 8S. 1864, p. 214, fig. 8 4, 1, 2), 
are very like those of this Rosherville specimen. In Megaptera 
(p. 210, fig. 7a) and in Stbbaldius (p. 224, figs. 16, 17, 18), how- 
ever, they are quite characteristic of the genus. 
The body of the third rib is on the whole much the same as the 
second, except that the sternal extremity tapers more gradually. 
The capitular process, so marked in the second, is here shortened, 
the head becoming rhomboidal in shape (fig. 4, no. 3). The arti- 
culating surface is not so extensive, and the tuberosity is less promi- 
nent ; the angle is at a greater distance from the vertebral extremity, 
and the neck is more marked. The fourth rib follows the general 
pattern of the second and third; but the head alters more in a line 
with the body (fig. 4, no. 4). The articulating surface is shorter, 
more vertically placed, and less pointed below and within; the angle 
is more bulky, but not so sharp. The sternal tapering end is enlarged 
in width, and it has an increased backward curve. 
The fifth is narrower, but very similar to the fourth. The angle 
increases in distance, but is less acute. The sternal extremity is con- 
siderably bent inwards towards the cavity of the thorax. The sixth 
and seventh decrease in width ; otherwise the curves are very similar 
to the fifth. The eighth, ninth, and tenth agree pretty much with 
each other; the body becomes more rounded. The angle nearly 
disappears in the eleventh. The twelfth is like the eleventh, but 
