Aponileus Hu, 1963

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 : 10

Aponileus Hu, 1963

Type species. Aponileus latus Hu, 1963 , from the Padre Formation ( upper Floian ; Blackhillsian), El Paso Group, Franklin Mountains, western Texas, USA .

Other species. All are Blackhillsian (upper Floian) in age; Aponileus aasei n. sp. (Fillmore Formation; probably Pseudocybele paranasuta Zone ); A. belkaae n. sp. (Wah Wah Formation; " Pseudocybele nasuta Zone "); Bolbocephalus glaber Poulsen, 1927 (Nunatami Formation, northwest Greenland); A. laikaae n sp. (Fillmore Formation; Presbynileus ibexensis Zone ); A. strelkaae n. sp. (Wah Wah Formation; " Pseudocybele nasuta Zone "); A. ugolekae n. sp. (Wah Wah Formation; " Pseudocybele nasuta Zone "); A.? veterokae n. sp. (Wah Wah Formation; " Pseudocybele nasuta Zone ").

Diagnosis. Glabella low and large, anteriorly expanded and occupying most of cranidial area; frontal areas small; preglabellar field absent, glabella abutting anterior border medially; palpebral lobes very large; most dorsal surfaces covered with dense raised line sculpture of various morphologies; librigena with large eye, narrow field, and flattened, blade-like genal spine (lost in some species); thorax of ten segments (known from only one species); pygidium wide and short (sag.), with either vestige of posteromedian spine in at least smaller specimens or with robust posteromedian spine.

Discussion. The broad, forwardly expanded glabella, huge palpebral lobes, and blade-like genal spine are an unusual combination for a bathyurid, and Aponileus is a distinctive clade. The only closely similar taxon is Psephosthenaspis Whittington, 1953 , to which, early in the project, we considered assigning the species. Although the genera are possibly related, they appear to be separate clades. The species of Psephosthenaspis most similar to those of Aponileus is P. glabrior Fortey and Droser, 1996 . It is revised on the basis of new silicified material below, and facilitates comparison of the genera and evaluation of their relationship (see genus discussion of Psephosthenaspis below).