ANATOMY OF MEGAPTERA LONGIMANA. 175 



11. The nipple-like process projects more in B. musciilus, pro- 

 jecting for f the length of the lamella; in Megaptera projecting 

 for about J the length of the lamella. The depression between 

 the nipple-like process and the lamella is narrower in B. miiscu- 

 lus. 12. The form of the bone behind the nipple-like process is 

 different. There is more of the bone behind the process in B, 

 musculus ; but what is most distinctive here is, that the inferior 

 border in B. musculus is carried farther round, to the level of the 

 base of the nipple-like process, and as a thick crest; while in 

 Megaptera the border forms a sharp peak at about the middle of 

 the posterior end of the bone. 



Periotic. — In Megaptera, the dimensions of the periotic bone 

 are, in inches — anterior division, length 4-J-, transversely 4, 

 height 2| — j^ost^rior division, length 7f ; height 2i anteriorly, 

 5 at the middle ; thickness 1 h above, below about ^ inch. The 

 inner surface of the wing-like posterior division is very rough on 

 its upper half; on its lower half it is concave vertically and 

 comparatively smooth, but is again roughened and thickened at 

 the lower free border. The whole external surface is strongly 

 streaked in the direction of the wing, the ridges curved, con- 

 vexity downwards. The whole wing is slightly bent on its axis, 

 concavity on the outer surface. Upper border a little concave 

 for 4| inches (then broken for 3 inches), lower border very con- 

 vex for 6 inches (then broken off). There is no trace of separate 

 development of the upper and lower parts of the wing.^ The 

 posterior junction between the periotic and tympanic is 1 inch 

 in breadth (outwards and backwards), in thickness f, thinner 

 behind ; the anterior junction is 1 inch antero-posteriorly, in 

 thickness | inch in front, jlg inch behind. 



Meatus externus and Tympanum. — In Megaptera, the 

 irregularly square-shaped meatua externus, included between 

 the tympanic and periotic and their two junctions, measures, 

 at its outer end, vertically 1 to 1^ inch ; antero-posteriorly, 

 at the lower part f inch, below the middle nearly -^r inch less, 

 owing to the backward curve of the lamella. The upper 

 boundary, formed by the periotic, is a little concave; the 

 posterior boundary, formed by the posterior junction, is a little 

 concave and is smooth ; the lower boundary, formed by the 

 1 See note, page 1S7. 



