21.   The ventral arm plates are an irregular pentagonal or hexagonal shape, often keeled, with the distal edge sometimes indented.

22.   The ventral arm plates are nearly pentagonal with a distinct convex distal edge textured with layers of calcite forming a concentric pattern.

23.   The ventral arm plates are not contiguous.

24.   The ventral arm plates are pentagonal often with a rounded distal edge, and are separated.

25.   The ventral arm plates are pentagonal with a wide distal edge, and contiguous on proximal arm segments.

26.   The ventral arm plates are pentagonal with an acute proximal angle, a slightly indented distal edge, and separated from one another.

27.   The ventral arm plates are pentagonal with the distal edge rounded and contiguous at least proximally.

28.   The ventral arm plates are pentagonal, broader than long and separated.

29.   The ventral arm plates are pentagonal, the distal edge is convex but indented in the middle.

30.   The ventral arm plates are small, pentagonal with a rounded distal edge, sometimes the distal edge is indented.