Chotecops cf. hoseri ( HAWLE et CORDA, 1847)

Budil, Petr & Mergl, Michal, 2019, Trilobite Assemblage Of Calceola - Bearing Beds In Acanthopyge Limestone (Choteč Formation, Middle Devonian, Eifelian, Prague Basin, The Czech Republic), Fossil Imprint 75 (1), pp. 79-91 : 81

Chotecops cf. hoseri ( HAWLE et CORDA, 1847)

Text-fig. 3a–f

M a t e r i a l. Eight incomplete cephala, six pygidia, numerous isolated fragments of cephala, pygidia and thoracic segments, two incomplete cheeks with preserved visual surface of the eye. Internal moulds and their counterparts, twenty five total remnants.

R e m a r k s. Preservation of even the best-preserved remains of phacopid exoskeletons does not allow positive determination of material to the species level, but it shares most features with Chotecops hoseri ( HAWLE et CORDA, 1847) . The angle of divergence in axial furrows is, however, slightly larger in the studied material (67°), but this value is barely larger than the upper limit of the variation range (60–65°) previously known in this species ( Chlupáč 1977: 53); this feature may have also been slightly affected by deformation. In the studied samples, the maximal number of lenses in the dorso-ventral row of the eye reaches 6 (5) ommatidia (in two young holaspid specimens, see Text-fig. 3d and younger unfigured specimen CGS MM 575), which fits well with description of Chotecops hoseri by Chlupáč (1977: 53). A lesser maximal number of ommatidia in a dorso-ventral row in the younger specimen can be explained by its early ontogenetic stage. In the largest specimen, the number of dorso-ventral rows in an eye is 17, and some are clearly missing (broken off). Following Chlupáč (1977), specimens of Chotecops hoseri should reach 18 dorsoventral rows. Pygidia correspond with C. hoseri in number of ribs (4–5, 6 in large specimens only; see Chlupáč 1977)), by their PL/PW ratios, and by prominent effacement of pleural furrows, except for the first one (two) pairs. The exact number of axial rings in studied specimens remains unknown because of poor preservation, but certainly exceeds four well-expressed rings. The studied remains differ from Chotecops auspex CHLUPÁČ, 1971 , also rarely occurring in the Acanthopyge Limestone ( Chlupáč 1971, 1977, 1983), in having slightly larger eyes with more dorsoventral files of ommatidia, and by better expressed pygidial segmentation (much effaced in C. auspex ). However, the observed angle of divergence in cephalic axial furrows fits better to the latter-mentioned species.