86 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



Oligocene of St. Domingo and Panama. Tampa silex beds at Bal- 

 last Point, Tampa Bay, Florida, U. S. Nat. Mus. No. 165095. 



This species has the cancellate structure of Oniscidia and a deep 

 recurved sulcus at the posterior end of the aperture. Its recent 

 analogue appears to be M. dennisoni Reeve, of the lesser Antilles. 



Family STROMBIDAE. 



Genus ORTHAULAX Gabb. 



Orthaulax Gabb, Proc. Acad. Nat. Sci. Phila., vol. 24, p. 272, pi. 9. figs. 3, 4. 



1872; Geol. St. Domingo, p. 274, 1873.— Guppy, Quart. Jouru. Geol. 



Soc. London, Nov. 1876, p. 520, pi. 28, fig. 8.— Tryon, Manual, vol. 2, 



p. 192, 1883.— Dall, Trans. Wagner Inst., vol. 3, pt. 1, p. 169, 1890. 

 Hippochrencs (part) Zittel, Tr. de. Paleout., vol. 2, p. 258, 1887. 

 Wagncria PIeilpbin, Trans. Wagner Inst., vol. 1, p. 105, pi. 15, figs. 36, 



36a, 1887. 



This genus is the most characteristic and typical of those belong- 

 ing to the Middle Oligocene of our southern coastal plain and the 

 Antilles, including Middle America. It does not appear in the 

 Vicksburgian fauna or the Nummulitic Ocala beds of Florida; it 

 seems to have become extinct before the development of the Oak 

 Grove, Florida, fauna. So far it has been recognized in the Mid- 

 dle Oligocene of Santo Domingo, Cuba, Antigua, the Canal Zone 

 of Panama, the Tampa silex beds, the Oligocene of Bainbridge, 

 Georgia, and the lower bed at Alum Bluff, with its stratigraphically 

 equivalent marl of the Chipola River, Florida. It is not known 

 from the Bowden beds of Jamaica, which are doubtless younger 

 than the Haitian Oligocene explored by Gabb, if indeed the latter 

 be not divisible into several distinct horizons. 



But the range in time appears so narrow and the genus so sharply 

 characterized that, according to our present knowledge, the dis- 

 covery of a species of Orthaulax in a Tertiary fauna may be taken 

 as positive proof of its Middle Oligocene age. 



The type of the genus is O. inornatus of Gabb, of which only 

 immature specimens have been figured as above noted; a figure of 

 the upper part of a mature individual is given herewith. No fully 

 complete specimen has yet been collected of this species, but the 

 form of either of the two other Florida species is well known, and 

 they may be discriminated without the slightest difficulty. 



ORTHAULAX INORNATUS Gabb. 



Plate 11, fig. 4. 



Orthaulax inornatus Gabb, Proc. Acad. Nat. Sci. Phila., vol. 24, p. 272. 

 pi. 9, figs. 3, 4, 1872. — GxTPPY, Quart. Journ. Geol. Soc. London, Nov. 

 1876, p. 520, pi. 28, fig. 8. 



Oligocene of Santo Domingo, Gabb (under the old appellation 

 of "Miocene") ; of the limestone at White Beach, Florida; and of 



