FAUNA OF ORTHAULAX PUGNAX ZONE. 115 



Florida, Dall; and in the equivalent lower bed at Alum Bluff on 

 the Chattahoochee River. Also in the Miocene of Duplin County, 

 North Carolina; Burns. U. S. Nat. Mus. No. 165140. 



This appears to be the precursor of the recent Fissuridea dlter- 

 nata Say, but does not attain so large a size, judging by the speci- 

 mens so far collected. 



Genus FISSURELLA Bruguiere. 



Subgenus CREMIDES H. and A. Adams. 

 FISSURELLA (CREMIDES) CERYX, new species. 



Plate 1. figs. 10. 11. 



Shell small, thin, subconic, basal outline rounded quadrate, the 

 anterior portion slightly wider; apex within the posterior third of 

 the length ; apical opening narrow, centrally slightly widened ; sculp- 

 ture of flattish radial riblets (about three to a millimeter) with sub- 

 equal interspaces, in most of which there are traces of a single much 

 finer radial thread; concentric sculpture of rather marked incre- 

 mental lines, which are not close set and which feebly inbricate the 

 riblets in passing over them; base (in the type) slightly arcuate, the 

 ends more produced than the central portions; interior smooth 

 except for a faint, muscular impression, the aperture not showing 

 any callus on the interior margin; basal margin feebly crenulated 

 by the ends of the riblets. Length 9.5 mm., height 4 mm., maxi- 

 mum diameter 7.1 mm.; the posterior margin of the aperture in 

 front of the posterior end of the shell 2 mm. 



Tampa silex beds, Ballast Point, Tampa Bay, Florida; one speci- 

 men collected by E. J. Post. U. S. Nat. Mus. No. 165109. 



Order POLYPLACOPHORA. 

 Family CHITONIDAE. 



Genus ISCHNOCHITON (Gray). 



Ischnochiton Gkay, Proc. Zool. Soc. London, 1847, p. 126. — Shuttleworth, 

 Berner Mitth., 1853, p. 66.— Pilsbry, Man. Concla., vol. 14, p. 86, 1882.— 

 Dall. Trans. Wagner Inst., vol. 3, pt. 2, p. 434, 1892. Type, Chiton 

 textilis Gray, South Africa. 



ISCHNOCHITON TAMPAENSIS Dall. 



Plate 3, figs. Sa. Sh. 



Ischnochiton tampaensis Dall, Trans. Wagner Inst., vol. 3, pt. 2, pi. 23, 

 fig. 23, 1892. 



Tampa silex beds, at Ballast Point, Tampa Bay, Florida ; Dall and 

 Crosby. U. S. Nat. Mus. No. 112607. 



In the absence of the tail valve and the armature of the girdle this 

 species can not be referred to its particular section of the genus. 



