Aponileus strelkaae, Adrain, 2012

Adrain, Jonathan M., 2012, The Lower Ordovician (upper Floian) bathyurid trilobite Aponileus Hu, with species from Utah, Texas, and Greenland 3293, Zootaxa 3293 (1), pp. 1-67 : 20-21

Aponileus strelkaae n. sp.

Plate 11, Plate 12, figs 1–20, 22–24

2009 Bathyuridae gen. nov. 6 sp. nov. 3; Adrain et al., p. 575.

Material. Holotype, cranidium, SUI 129298 (Pl. 11, figs 1, 2, 4, 6, 9), and assigned specimens SUI 129299–129311 , from Section J 28.1 m, Wah Wah Formation ( upper Floian ; Blackhillsian; " Pseudocybele nasuta Zone "), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. After Strelka.

Diagnosis. Frontal glabellar lobe not as broadly expanded as in other species; dorsal surfaces with very dense, fine, and crowded raised line sculpture, tubercles faint on rear of glabella in large specimens, best expressed on LO; genal spine relatively short, with narrow dorsal flattened surface; pygidium small and narrow, with three rings but third ring tiny and visible mainly ventrally, completely lacking expression of posteromedian spine even in smaller specimens.

Description. Aponileus strelkaae is similar enough to the slightly older A. belkaae that extended written description would be redundant; all differences between the species are noted in the following differential description. Cranidium with anterior sections of facial sutures of large specimens anteriorly convergent, versus laterally bowed; cranidium considerably narrower across anterior border; glabella much narrower anteriorly, not strongly waisted, and considerably more dorsally vaulted; axial furrows essentially straight and oblique, versus bowed laterally anteriorly; librigenae with shorter genal spine (comparison is hampered by the fact that the spine is incomplete in many specimens, but compare the intact and similarly sized specimens of Pl. 8, fig. 1 and Pl. 12, fig. 1); librigenal field slightly narrower, with denser and more closely spaced anastomosing line sculpture; pygidium relatively smaller, narrower relative to length, with third segment poorly versus obviously expressed dorsally, and with much finer and denser raised lined sculpture on all surfaces; although there is some overlap, the second pleural furrow is very weakly expressed on all specimens of A. strelkaae whereas it is well expressed on many specimens of A. belkaae .

Discussion. Apart from the differences noted in the differential description, A. strelkaae is very similar to the slightly older A. belkaae . As noted several times above, reduction to three pygidial segments is a very unusual feature. Aponileus strelkaae extends this trend by greatly reducing the third segment. In dorsal view, it is not clearly differentiated from the terminal piece, but ventral views (Pl. 12, figs 15, 18) show that the third segment is definitely present.