122 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



(3.) In the third degree of complexity the vertical plate is revolute 

 anteriorly, and (as seen from above) is sub-triangular or cylindroid in 

 form. It retains upon its median surface two supplemental horizontal 

 or oblique scrolls. The outer (lateral) scroll is present. 



The vertical plate may project well in advance of all the other parts, 

 or may be but slightly longer than they. No union exists between the 

 outer (lateral) scroll and the vertical plate of the frontal bone in the 

 orbit. Examples, Vespertilionidoe, the genus Molossus, its congeners, and 

 Noctilio. Natalus is remarkable for lacking the outer (lateral) scroll. 



In Molossus, Nyctinomus, and Noctilio the vertical plate projects 

 scarcely at all in advance of the median supplemental scrolls, and never 

 appears on the median surface below the level of the scrolls. In Ves- 

 pertilionidcB it forms a conspicuous tapering process. It is seen below 

 the plane of the supplemental scrolls in Atalapha novehoracensis and 

 Vesperus noctivagans. 



(4.) The vertical plate is short and ends abruptly anteriorly. It is 

 visible beneath the supplemental scrolls on the median surface. The 

 outer (lateral) scroll is as long as the vertical, and is united to the ver- 

 tical orbital plate of the frontal bone. Example, the genus Taphozous. 



(5.) The vertical plate is produced in advance of the position of the 

 supplemental scrolls, as in the last-named group, but is compressed from 

 side to side as seen from above, and is not revolute. It bears upon 

 its median aspect posteriorly a lobule. The supplementary scrolls in 

 general appearance are much as in the Vespertilionidoe. The lateral 

 scroll is cylindroid. Examples, the Phyllostomidce. 



In Desmodus, the lobule upon the anterior portion of the vertical 

 plate is relatively large. 



(6.) The vertical plate is projected far in advance of the supplemen- 

 tal scrolls, which are horizontal in position and four in number. The 

 lateral scroll is more or less adherent to the vertical plate, or by its 

 outer border to the frontal bone. Examples, the Pteropidce. 



The Pteropidce, JVycteridce, and some Phyllostomidoe have a horizontal 

 septum passing transversely from the under free edge of the vertical 

 plate (as it lies beneath the lowest median supplemental scroll) to the 

 nasal septum. The olfactory surface in such forms is thus withdrawn 

 from the respiratory currents, since no direct outlet exists at the pos- 

 terior nares. 



The above descriptions have been drawn, for the most part, from 

 specimens in the fine collection of the Museum of Comparative Zoology, 

 Cambridge, Mass. 

 February, 1880. 



