1917.] NATURAL SCIENCES OF PHILADELPHIA. 177 



as wide as the smooth concave interval which do not quite extend 

 to the suture below, and terminate abruptly at the periphery. There 

 are ten ril^s on the penult whorl. Base smooth. The aperture is 

 trapezoidal; columella verj' slightly sinuous. 



Length 2.8, diam. 0.5, length of aperture 0.4 mm.; 9^ post-nuclear 

 whorls. 



Type No. 3024, A. N. S. P. 



This is the most slender of the known Santo Domingan species, 

 further distinguished by its few coarse ribs. 



Turbonilla (Nisiturris) undecimcostata n. sp. 



The shell is slender with bulimoid nucleus; subsequent whorls 

 convex, sculptured with narrow, straight vertical ribs separated by 

 concave intervals about twice as wide as the ribs, and under strong 

 magnification showing extremely fine and faint vertical and spiral 

 striae. The concave intervals terminate rather abruptly just above 

 the suture and at the periphery. On the penult whorl there are 

 eleven ribs. The aperture is subtrapezoidal. Columella thick and 

 very slightly sinuous. 



Length 3.3, diam. 0.7, length of aperture 0.5 mm.; 9| post-nuclear 

 whorls. 



Type No. 3023, A. N. S. P. 



Turbonilla (Nisiturris") pertenuis Gabb. 



Turbonilla pertenuis Gabb, Trans. Am. Philos. Soc, XV, 1873, p. 226. 



An extremely slender species. Nuclear shell bulimoid; sub- 

 sequent whorls at first rather strongly convex gradually becoming 

 less convex, the lower ones somewhat flattened laterally, with sculp- 

 ture of strong, rounded vertical ribs parted by slightly wider, smooth, 

 concave intervals, the rounded lower ends of which are a little above 

 the lower suture, leaving a very narrow smooth band on each whorl. 

 There are twelve ribs on the penult whorl. Base smooth, convex, 

 the columella is thin and slightly sinuous. 



Length 4, diam. 0.7, length of aperture 0.6 mm.; 11 post-nuclear 

 whorls. 



Type No. 3030, A. N. S. P. 



Turbonilla (Nisiturris) contexta n. sp. 



The shell is very slender with bulimoid embryo; subsequent whorls 

 convex at first, the later ones distinctly flattened, sculptured with 

 vertical rounded ribs, 15 on the penult whorl, slightly narrower than 

 the concave intervals, and extending from suture to suture. Under 

 the compound microscope the intervals are seen to have a minute 



