The lichid trilobiteRadiolichasin the Silurian of Arctic Canada and Gotland, Sweden

Abstract

Radiolichas has been a poorly known and exclusively Devonian genus of very limited diversity. Radiolichas raydaviesi sp. nov. and R. davedaviesi sp. nov. are the best-known members of the genus, and extend its stratigraphic and geographic range to the Wenlock of the central Canadian Arctic. A further Silurian occurrence is an unnamed species from the Wenlock Slite Beds of Gotland, Sweden. Radiolichas is most similar to Dicranogmus. Together, the genera lack any of the robust trochurine apomorphies (linear pygidial postaxial ridge, prominent pygidial border, prominent cranidial fossula) and appear to fall outside the phylogenetic structure of that subfamily. They are similar to members of the Tetralichinae, particularly in pygidial features, but lack the composite cranidial lobe characteristic of that subfamily. Their systematic position is presently unresolved. J. M. ADRAIN & L. RAMSKOLD 96*00'Dundaa U 94 -00'

Validity and composition of the Silurian trilobite genera Borealarges and Dicranogmus, with new species from the Canadian Arctic

“…REMARKS: As noted earlier in the text, Thomas and Holloway (1988) were not convinced that Perry and Chatterton's (1977) association of sclerites in their new Dicranogmus skinneri was correct. Adrain and Ramsköld (1996) gave reasons for confidence in the association, and it is confirmed by revision of D. skinneri and description of D. wynni. Briefly, cranidia and pygidia of species of Dicranogmus occur at all sampled horizons of the Cape Phillips Formation.…”

“…18, fig. 3), along with a Borealarges pygidium, which is almost certainly that of simplex. Adrain and Ramsköld (1996) clarified the systematic position of Dicranogmus, showing that it bears considerable, likely synapomorphic, similarities to Radiolichas, and that the status of the genera as Trochurinae (of which Borealarges is clearly a member) is, in the present state of knowledge, ambiguous. Vank (1999) reproduced Voká's photographic plate, with the addition of a single illustration of another cranidium collected by Voká and belonging to simplex (Vank 1999, pl.…”

“…Their description was begun by Perry and Chatterton (1977), who named three new lichid species. Adrain (1994) proposed the new trochurine genus Borealarges, while Adrain and Ramsköld (1996) have described the oldest known members of Radiolichas Reed 1923. Adrain andRamsköld (1996) gave the stratigraphic ranges of all Cape Phillips Formation lichid species for which at least some sclerites had been illustrated.…”

“…As a result, he concluded that Borealarges is a junior synonym of Dicranogmus. Vank did not cite Adrain and Ramsköld's (1996) paper.…”

THE EXTRAORDINARY TRILOBITE FENESTRASPIS (DALMANITIDAE, SYNPHORIINAE) FROM THE LOWER DEVONIAN OF BOLIVIA

“…see Holloway 1996; Basse et al. 2007; Feist and Lerosey‐Aubril 2008), the cheirurid Deiphon (see Lane 1971; Chatterton and Perry 1984) and the lichid Radiolichas (see Adrain and Ramsköld 1996; Campbell and Chatterton 2006), the inner, articulated portion of the thoracic pleurae and the corresponding part of the pygidial pleural region are very narrow, and the remainder of the pleurae are reduced to free spines. The fenestrae would have opened directly above the filamentous gill branches or exites of the biramous appendages, and their function may have been to allow circulation of oxygen‐bearing water so that respiration could have been maintained while the animal was fully enrolled.…”