Pseudoniscus roosevelti, Clarke, 1902

Bicknell, Russell D C, Amati, Lisa & Ortega-Hernández, Javier, 2019, New insights into the evolution of lateral compound eyes in Palaeozoic horseshoe crabs, Zoological Journal of the Linnean Society 187 (4), pp. 1061-1077 : 1066

Pseudoniscus roosevelti

The other synziphosurine taxon from the Late Silurian-aged (Ludlow, sensu Gupta, 2014) Vernon Shale in New York State, USA was originally described by Clarke (1902) as being blind. Ruedemann (1916) investigated more specimens of Pseudoniscus roosevelti than Clarke and suggested that LCEs were present, but the legitimacy of his observations was doubted by Eldredge (1974), Bergström (1975) and, more recently, by Krzemiński et al. (2010). Re-examination of NYSM 19112 led us to the identification of a prominent reniform LCE preserved on the left side of the prosomal shield ( Fig. 4C, D). There is no evidence for the presence of ophthalmic ridges on the prosoma. The LCE is 2.1 mm from the anterior, 4.5 mm from the posterior, 2.2 mm from the lateral boarders and 2.5 mm from the prosomal midline. The LCE outline is darker than the surrounding specimen, and most of the posterior 0.3 mm section is completely pigmented. The eye is 0.5 mm wide and 0.9 mm long. Possible evidence for ommatidia is also preserved ( Fig. 4D), consisting of a quadruplet of circular lenses on an isolated lateral patch of dark material, with another lens triplet on the anterolateral margin of the preserved eye.