Exterior.—The test is of medium size. Adult specimens have a length ranging from 4.2 mm. to 6.5 mm. and a diameter of 1.6 mm. to 2.5 mm. The form ratio varies from 2.3:1 to 2.9:1 and averages 2.66 :1. The shape of the test is fusiform with straight axis and sharply rounded to somewhat bluntly pointed ends. The lateral slopes are gently convex to somewhat concave. Equatorial section.—Adults show from five and one-half to seven and one-half whorls. The heights of the whorls are 0.04 mm. to 0.06 mm. in the first whorl, 0.05 mm. to 0.09 mm. in the second, 0.08 mm. to 0.12 mm. in the third, 0.12 mm. to 0.18 mm. in the fourth, 0.15 mm. to 0.22 mm. in the fifth, 0.18 mm. to 0.25 mm. in the sixth, and 0.21 mm. to 0.26 mm. in the seventh, as measured near the end of each whorl. The septa number 9 to 14 in the first whorl, 11 to 18 in the second, 15 to 22 in the third, 17 to 26 in the fourth, 19 to 27 in the fifth, 22 to 30 in the sixth, and 26 to 32 in the seventh. The proloculum has an outside diameter of 0.09 mm. to 0.18 mm. The thicknesses of the wall are 0.01 mm. to 0.02 mm. in the first whorl, 0.015 mm. to 0.025 mm. in the second, 0.02 mm. to 0.03 mm. in the third, 0.022 mm. to 0.04 mm. in the fourth, 0.03 mm. to 0.04 mm. in the fifth and sixth, as measured near the end of each whorl. The wall is composed of outer and inner tectoria, tectum and diaphanotheca. Axial section.—The fluting is moderate to strong across the midzone and strong toward the ends of all specimens. The chomata are prominent in all whorls. The tunnel is moderately wide, having values of 20° to 25° in the first whorl, 18° to 20° in the second, 21° to 30° in the third, 24° to 31° in the fourth, 28° to 40° in the fifth, and 33° to 50° in the sixth. A few septal pores are seen in occasional specimens, but for the most part they are lacking. Discussion.—This species is distinguished from F. euryteines mainly by its much wider tunnel, its slightly greater length, and its greater form ratio. These features and its scarcity of septal pores separate it from F. rockymontana Roth and Skinner. Occurrence.—Commonly associated with F. euryteines and Wedekindellina euthysepta in the lower half of the Magdalena formation in the Socorro Mountains, Lemitar Mountains, Sangre de Cristo Mountains east of San Geronimo and also northwest of Montezuma Hot Springs, Magdalena Mountains near Kelly, and the north end of the Oscura Mountains on the Bursum Ranch. (Needham (1937)).