In rearranging the Carboniferous fossils in the Woodwardian Museum, I met with a specimen labelled Aihyris, n.sp., which reminded me of the form described by De Koninck as Terebratula serpentina. On careful examination I am convinced that it belongs to this species, and the following is a description of our specimen:— Shell subovate, terebratuliform, widest at about one-third its length from its anterior edge. Valves moderately convex, slightly flattened anteriorly, and devoid of sinus and fold; margin entire and regular. Ventral valve a little less deep than dorsal valve, and furnished with a slightly recurved beak truncated by a large circular foramen, bordered in front by a pair of deltidial plates. Surface of both valves ornamented with straight, radiating, very faint ribs, 60 to 70 in number, arranged in a regular close series separated by weak narrow furrows. Some of the ribs bifurcate at about half their length, and those near the hinge-line curve gently backwards. Shell substance finely punctate. Concentric strife of growth are distinct on both valves. Length, 25 mm.; breadth, 22 mm.; dorsiventral diameter, 12 mm.