Shell slender, fusiform, attenuated toward the apex; rather solid and strong; brown, somewhat glossy; very closely and finely striate, the striae a little closer on the back of the last whorl. Whorls 9,5 or 10, the first one globose, sometimes self-amputated. The attenuated early whorls are very convex, the later ones less so, and the last whorl is somewhat flattened laterally, with a noticeable impression marking the position of the principal plica. The aperture is trapezoidal-ovate, somewhat oblique, the peristome reflexed, slightly thickened, con¬tinuous and well raised across the parietal wall. The superior lamella is small, marginal and oblique, continuous with the spiral lamella, which is very high within and penetrates across the ventral side. The inferior lamella recedes deeply, and within the back ascends obliquely, and is nearly straight. It is far smaller and lower than the spiral lamella, but penetrates as deeply. The subcolumellar lamella emerges to the lip-edge. The principal plica is very long, reaching nearly to the peristome, and penetrating inward to a point above the sinulus. The lunella with the upper and lower palatal plicae is shaped like the letter I, and is nearly ventral in position.
Length 15.7, diam. 3 mm.
Length 15.3, diam. 3.4 mm.
The clausilium is long and narrow, parallel-sided, obliquely rounded distally, and very deeply excised on the columellar side of the filament.
Yasuda-mura, Tosa. Types No. 87,576, A. N. S. P., from No. 1,011 of Mr. Hirase's collection.
In this Hemiphaedusa of the group of C. aulacophora the plicae and lamella penetrate very deeply—across the ventral side—and the lunella stands in a ventral position, above the columellar margin of the peristome. In C. aulacophora and C. pigra the lunella is lateral, but of the same shape. C. ventriluna is very closely related to C. caryostoma and C. c. jayi, which have the armature similarly deep-seated; but neither of these forms has a perfect lunella uniting the two palatal plicae.
The clausilium is not thickened distally as in Tyrannophaedusa, but otherwise C. ventriluna has much in common with C. (Tyr.) aurantiaca.
Other specimens from Tsushima, Awa (Shikoku), are smaller than those from Yasuda-mura, and the superior lamella is either separated from the spiral lamella or but weakly connected therewith. The principal plica is a little shorter inside. In some of the specimens the subcolumellar lamella emerges to the lip-edge, and is bounded by furrows. In others it is immersed or very feebly and slightly emerges. These shells are No. 1,187 of Mr. Hirase's collection.