90 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



gocene limestone of Jacksonboro, Screven County, Georgia ; Vaughan. 

 U. S. Nat. Miis. No. 165105. 



This species does not belong to the typical group of the genus, but 

 in the present confused state of the nomenclature of Cerites I use the 

 generic name in its widest sense. 



CERITHIUM PRAECURSOR Heilprin. 

 Plate 5, fig. 5 ; plate 12, fig. 26. 



Cerithium praecursor Heilprin, Trans. Wagner Inst., vol. 1, p. 114, pi. 16, 

 fig. 58, 1887.— Dall, Trans. Wagner Inst., vol. 3, pt. 2, p. 285, 1892. 



Shell small, thin, slender, with about 9 sculptured whorls, the 

 nucleus defective; suture distinct; axial sculpture of (on the penulti- 

 mate whorl 11) small rounded riblets, with wider interspaces, not 

 continuous over the spire and slightly retractive, they practically be- 

 come obsolete at the periphery; besides these the axial sculpture 

 comprises only rather marked incremental lines and the usual varices 

 at the beginning of the second half of the last whorl, and at the 

 aperture; spiral sculpture of (on the spire 3 and on the last whorl 

 6) primary spiral threads with wider, nearly equal interspaces, the 

 threads equal and slightly swollen where they cross the axial riblets ; 

 between these, in the interspaces, are two or three much finer equal 

 threads (hardly apparent in the figure) equally spaced, and on the 

 back of the canal 5 or 6 close-set coarser threads; aperture sub- 

 lunate with a narrow sulcus between a subsutural nodule, and the 

 outer lip behind; inner lip continuous, with a smooth free edge; 

 outer lip smooth internally with a slight varical thickening behind; 

 canal wide, very short, slightly recurved, with no sulcus at the base 

 of the whorl behind it. Length 12 mm., maximum diameter 4.5 mm. 



Tampa silex beds at Ballast Point, Tampa Bay, Florida. Various 

 collectors. U. S. Nat. Mus. Nos. 112523 and 165106. 



This seems to have been an ancestor of such forms as C. muscarum 

 Say. It has also been found in the shape of molds in the limestone 

 of Wakulla County, northwest Florida, near Wakulla. 



CERITHIUM, sp. indet. 

 Cerithium sp. indet, Dall, Trans. Wagner Inst., vol. 3, pt. 2, p. 285, 1892. 

 Tampa silex beds at Ballast Point, Tampa Bay, and also in the 

 Wakulla limestone, Florida. U. S. Nat. Mus. No. 113371. 



The specimens were too imperfect for description but not identical 

 with the preceding. 



CERITHIUM PLECTRUM, new species. 



Plate 9, fig. 3. 



Shell small, solid, comprising about 5 whorls without the (decol- 

 late) nucleus which seems to have been smooth; spiral sculpture: 



