CRETACEOUS FOSSILS. 261 



plain, marked only by obsolete lines of growth, and ornamented 

 by more or less sinuous, broken, irregular bands of color, longi- 

 tudinally disposed, and sometimes entire, sometimes zigzag, 

 branching, anastomosing and running out Aperture subellip- 

 tical ; outer lip sinuous ; inner lip heavily incrusted. 



Figure, natural size. 



Easily recognized by its elongate form and nearly flat sides, and by the unusual 

 circumstance of the retention of its color. Every specimen I have seen shows the 

 colored pattern when the surface is wet, and most of them retain it so strongly as 

 to show it even when dry. 



Considerable confusion has arisen from a want of a clear understanding of the 

 relations of d'Orbigny's genus Chemnitzia to Turbonilla of Risso. I believe Mr. 

 Conrad was the first author to call attention to the fact, that good points of differ- 

 ence exist between the two. Chemnitzia is essentially a genus of comparatively 

 large shells, all fossil, and which seem to be confined to Secondary rocks. They 

 have thick shells, and are usually more or less angulated, with heavily incrusted 

 inner lips. Turbonilla seems to have originated in the later Tertiaries, and attains 

 its maximum development in the present seas. It contains only small shells, many 

 of them being almost microscopic ; they are usually thin, and the inner lip is little 

 or not at all incrusted. 



C. Texana, Roem., sp. 



(Scalaria Texana, Roem. ; Kreid. Tex., p. 39, pi. 4, fig. 11.) 



A smaller shell than the preceding ; characterized by rounded whorls, strong 

 longitudinal ribs, and smaller revolving ribs. It seems to be a rather rare shell. 



TYLOSTOMA, Sharpe. 1849. 

 Varigera, d' Orb. 1850. 



T. MUTABIL1S, n. S. 

 PI. 35, Fig. 6, a, b, c. 



Shell very variable in shape, according to age. In the very 

 young, subglobose or subovate; becoming more elongate in the 

 adult, and compressed in the very old ; apex elevated in average 

 specimens; whorls seven to seven and a half, rounded on the 

 sides, and usually more or less converging; suture deeply im- 



