1917.] NATUEAL SCIENCES OF PHILADELPHIA. 151 



and size, but the aperture is slightly narrower above, and except 

 close to the base there is no spiral striation. 



Length 10, diam. 4.6 mm. 



T^-pe No. 3193. 



Retusa biforis n. sp. 



The shell is perforate at both ends, cylindric, smooth. Above it 

 tapers to an angle around the concave summit, which has a small 

 perforation. Aperture is about twice as wide in the lower as in the 

 upper part. The lip recedes strongly at both ends. Columella 

 straight, the columellar margin somewhat reflected, the whorl narrowly 

 excavated below the perforation. 



Length 3, diam. 1.4 mm. 



Type No. 3192, A. N. S. P. 



Volvula ornata n. sp. 



The shell is moderately obese, tapering downward, with sculpture 

 of small axial folds near the summit, spiral impressed lines around 

 the base. Spine is moderately long, obtuse. 



Length 3.75, diam. 1.7 mm. 



Type and 7 other specimens are No. 3178, A. N. S. P. 



Volvula parallela n. sp. 



The shell is extremely fragile, slender, cylindric, showing extremely - 

 faint and fine spiral striation in the lower half. The spine rises well 

 above the lip, is rather short and acute. The columella is a little, 

 convex. 



Length 2.2, diam. 0.75 mm. (type). 



Length 3 mm. (largest specimen). 



All of the three specimens are somewhat broken. It is the most 

 fragile and slenderest Volvula we have seen. 



Type No. 3188. 



Volvula cylichnoides n. sp. 



The shell is rimate, oblong, the right side less convex than the left, 

 the surface smooth so far as can be seen. The lip rises high above 

 the vertex, which shows no trace of a spine, and is narrowly rounded 

 above. Columella nearly straight. 



Length 4.4, diam. 2 mm. 



Type No. 3177, A. N. S. P. 



This species appears to be closely related to the unfigured recent 

 V. aspinosa, but there is no trace of the rudimentary spine described 

 for that species. 



