1974 Hystrichosphaeridium sp. 2 of McIntyre, pl. 11, fig. 3 (non fig. 2).
1974 Hystrichosphaeridium sp. 3 of McIntyre, pl. 10, figs. 7–8.

Holotype. Plate 2, figure 10; GSCA slide no. P51225-05 (¼GSCC slide no. P5205-118H); coordinates 8.0x91.1; EF intersection of T57/circle with T57/3; Nunavut Palaeontology Collection no. NUPB 982; Q section; Twosnout creek, Bylot Island. Bylot Island formation.

Etymology. The epithet is from the Latin procerus, meaning slender, tall, long, in reference to the elegant nature of the processes and their distal extremities.

Diagnosis. A species of Hystrichosphaeridium with very slender, elegant processes, which distally have long slender aculeae that within individual processes are frequently interconnected. The nature of some processes distally is reminiscent of those in Oligosphaeridium pulcherrimum.

Comments. McIntyre (1974) illustrated two informal species, Hystrichosphaeridium sp. 2 (his pl. 11, figs. 2–4; only fig. 3 is assignable to Hystrichosphaeridium procerum) and Hystrichosphaeridium sp. 3 (his pl. 10, figs. 7–8), but did not describe either of them. We consider most of the illustrated specimens to be assignable to Hystrichosphaeridium procerum, although the specimen illustrated in McIntyre 1974(pl. 11, fig. 4) is a different, unnamed species.

Size. Holotype: central body width 48um; processes up to 28um. Range of eight specimens: central body length 24– 50um, central body width 26–48um, process length up to 30um, process width 1.5–4um.

Age. Early Campanian to early Maastrichtian.