Ivops, Sandford & Holloway, 2006

Sandford, Andrew C. & Holloway, David J., 2006, Early Silurian phacopide trilobites from central Victoria, Australia, Memoirs of Museum Victoria 63 (2), pp. 215-255 : 233

Ivops gen. nov.

Type species. Ivops wallanensis sp. nov. from the Bylands Siltstone (Wenlock), central Victoria .

Derivation of name. After the late Professor Ivo Chlupáč, Charles University, Prague. Gender masculine.

Diagnosis. L1 with lateral node very small and depressed, L2 short (exsag.). S2 containing deep pit adjacent to axial furrow, forming a notch in side of glabella. Anterior branch of S3 long, subparallel to axial furrow. Front of glabella overhanging anterior border. Eye relatively small, length (exsag.) approximately 30% sagittal cephalic length, its lower edge lying just above lateral border furrow anteriorly, visual surface without raised sclera. Lateral border furrow on fixigena continuous with posterior border furrow. Vincular furrow with weak notching laterally. Pygidium with weakly tapering axis constituting about 30% maximum pygidial width anteriorly, and with deep pleural and shallow but distinct interpleural furrows. Dense sculpture of bimodal tubercles on glabella.

Remarks. Ivops is known only from the type species. The genus closely resembles Ananaspis in glabellar and pygidial proportions, the short L2 (exsagittal length 80% that of L3), the continuity of the posterior border furrow with the lateral border furrow on the fixigena, the weak notching in the lateral part of the vincular furrow, and the depth of the pygidial pleural and interpleural furrows. The relatively small eye with its lower edge placed a short distance above the lateral border furrow and with a small number of lenses in the dorsoventral files are features comparable with species such as A. aspera and A. calvescens . Despite these shared features Ivops is unlike Ananaspis and other known Silurian phacopines in that S2 is deep laterally and contains an apodemal pit where it meets the axial furrow. This feature contrasts with the more typical phacopine morphology of a shallow S2 that is isolated from the axial furrow. A laterally deep S2 similar to that of Ivops is present in ʻ Paciphacops ʼ microps Chatterton, Johnson and Campbell, 1979 (type species of Kainops Ramsköld and Werdelin, 1991 ), from the upper Lochkovian to lower Pragian of New South Wales, but in that species S2 does not contain an apodemal pit and does not meet the axial furrow in all specimens. The relatively small eye of Ivops (the smallest of known Wenlock phacopids) is interpreted as an adaptation to a deep-water environment;see discussion in remarks on Berylacaste berylae gen. et sp. nov.