14 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



To arrive at just conclusions in such divisions it is of course neces- 

 sary to have a pretty thorough Imowledge of the fauna of eacli zone 

 or horizon; otherwise the really characteristic species of each zone 

 may not be recognized. 



The same facts are true of the Tertiary of the coastal plain of 

 the southeastern United States, but hitherto the number of mono- 

 graphic studies of particular faunas has been very small compared 

 with those which still remain to be investigated, and no exhaustive 

 arrangement of our marine Tertiary column can be reasonably ex- 

 pected for many years to come. It was in view of these facts that 

 in the tentative summary of our southeastern marine Tertiary, pub- 

 lished in 1898,^ the writer followed the method approved by the 

 International Geological Congress of 1889 and already adopted by 

 Marsh and other students of American vertebrate paleontology, by 

 referring to the subdivisions as " series," " groups," and " beds " and, 

 as far as possible, avoiding the indefinite and frequently misleading 

 term " formation." 



Some progress has been made since that time, and the European 

 method is beginning to be appreciated, though delayed by the paucity 

 of workers in the field of Tertiary invertebrate paleontology, and the 

 consequent insufficiency of our knowledge of the greater number of 

 our invertebrate Tertiary faunas. 



The fauna represented in the silex beds at Ballast Point, Tampa 

 Bay, Florida, which is the subject of this monograph, contains two 

 species of the remarkable genus Orthaulax Gabb ; one of these is rare 

 and was the type of the genus, named by Gabb O. inornata^ from 

 Santo Domingo specimens. The other, more abundant, is the 0. 

 pugnax of Heilprin. The genus first appears, so far as now known, 

 in this horizon, and both species are reported from the White Beach 

 limestone, Little Sarasota Bay, Florida; at least one or both have 

 been obtained from the lower part of the Oligocene beds in the Canal 

 Zone, Panama, and from the West Indian islands of Antigua and 

 Anguilla; while the genus was recognized by Dr. T. W. Vaughan 

 at Consolazion del Sur, Pinar del Rio, Cuba, and at Original Pond, 

 Thomas County, Georgia. The writer also obtained O. fugnax at 

 Bainbridge, Georgia, as did also Doctor Vaughan. 



The importance of these fossils in linking the Oligocene of the 

 West Indian, Isthmian, and Caribbean with that of the continent 

 is obvious. I have therefore designated the zone so represented as 

 the Orthaulax pugnax zone, with the typical locality at Ballast 

 Point, Tampa Bay, Florida, the only locality where the fauna has 

 been exhaustively studied. 



It is somewhat remarkable that Orhitolites floridana is exces- 

 sively rare in this zone, while extremely abundant in the zone above. 



1 Eighteenth Ann. Kept. U. S. Geol. Survey, pp. 323-348. 



