Icriodus alternatus alternatus Branson and Mehl, 1934

Fig. 5D–F.

Icriodus alternatus; Branson and Mehl 1934: 225–226, pl. 13: 4–6 [fig. 4 = lectotype]; Klapper 1975: 69–70, Icriodus pl. 3: 5, 6.

Icriodus alternatus alternatus Branson and Mehl, 1934; Sandberg and Dreesen1984:158–159,pl.2:5,11;seehereforfurthersynonymy.

Remarks.—The P 1 (Pa, I) element of Icriodus alternatus is straight to slightly curved; the middle row of denticles are low, compressed, or poorly developed, and may alternate with or be fused to outer denticles. The basal cavity is expanded to widely flared under the posterior third of element. Icriodus alternatus alternatus is distinguished from I. alternatus helmsi byaP 1 elementinwhichthecuspisalignedwith the medial denticles. Specimens from the upper Hanover Shale possess rounded median denticles fused to the lateral denticles. This morphology is suggestive of I. iowaensis Youngquist and Peterson, 1947, but the lateral and median denticles are not aligned, as well as the fact that no axial ridge connects the medial denticles.