24 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 85 



Collins in zone 10 of the Calvert formation, at the beach level 1 mile 

 south of Plumpoint on April 7, 1934. The specimen consists of a little 

 more than the proximal half of the bone, with the head missing but 

 with the lower part of the deltoid crest present. The shape is similar 

 to that of Sula piscator except for decidedly smaller size. The line of 

 attachment for the latissimus dorsi anterioris muscle is strong and 

 heavy, running for most of its course above the central axis of the, 

 bone when viewed from the side. 



i' "iffc' 



Figure 3. 



-Sula (Microsula) avita, new species : Left metacarpal, including profile views 

 of the proximal and distal ends. About natural size. 



In summary, the impression given by this fragmentary material 

 is that of a booby decidedly smaller than any of the living species. 

 In size it resembles most closely the fossil /Sula 'pygmaea of the 

 Miocene of Europe but differs from that species in the form of the 

 distal end of the humerus. 



The nearly obsolete pneumatic foramina, so prominent in modern 

 gannets and boobies, is remarkable, indicating that this pneumaticity 

 has been a more recent development than other characters that mark 

 this family. Data on this point from other Miocene sulids will be of 



