Slimonia

Abstract: The Silurian and Lower Devonian pterygotid eurypterids were the largest of all arthropods, but their origin and early evolution are poorly understood. Pterygotus? ventricosus from Kokomo, Indiana, is shown to be the most basal of the pterygotids and constitutes the sister taxon to the rest of the clade. P.? ventricosus has walking appendages similar to those of Slimonia, which is the sister taxon of pterygotids. There is no evidence in P.? ventricosus of the dorsal median pretelson carina characteristic of other pterygotids, but the taxon does have the typical pterygotid undivided genital appendage. The status of the iconic pterygotid character (and presumed synapomorphy), the enlargement of the chelicerae, is uncertain in the Kokomo pterygotid. All the diagnostic characters of pterygotids did not develop simultaneously. A new genus Ciurcopterus is erected to accommodate the Kokomo pterygotid and Pterygotus? sarlei Ciurca and Tetlie.

Abstract: Eurypterids from the Welsh Borderlands of England are redescribed from most available material. Hughmilleria banksii is here interpreted to represent a new genus. The poorly known Hughmilleria (?) acuminata (Salter, 1859 a ) is considered a junior synonym of H. banksii. Furthermore, Slimonia ? stylops is suspected to be a junior synonym of Salteropterus abbreviatus , although they are not formally synonymized as the location of the only known specimen of S. ? stylops is unknown. Morphological differences in carapace shape, eye position, walking leg, genital appendage and telson in H. banksii are noted compared to previous descriptions. A prosomal appendage earlier assigned to H. banksii is here assigned with caution to S. abbreviatus and the reported ‘segments’ in the posterior part of the telson of S. abbreviatus are shown to be cracks. The phylogenetic position of the new genus is inferred to lie between the Hughmilleria and the Slimonia / Salteropterus clades.

Abstract: The remains of Pterygoti appear to have been first found in the Upper Silurian beds of the Pentland Hills, during the time the Geological Survey were engaged surveying that district. This discovery was recorded by the late Mr Salter in the ‶Survey Memoir on the Edinburgh District,″ and consisted of the serrate base of one of the great swimming feet of Slimonia ( Pterygotus ) acuminata, Salter, obtained by the collector, Mr Gibbs, at Deerhope Quarry.* The next record is that of the late Mr G. C. Haswell, who obtained from near the Bavelaw Reservoir, six body segments and part of the bilobed telson of Pterygotus bilobus, Salter;† Mr Haswell also states that he found the serrate base of one of the jaw-feet of a species apparently allied to the form mentioned by Mr Salter, but smaller. These are, so far as I can ascertain, the only published records of Pterygoti remains from the Pentland Hills. Lately, Mr Henderson has drawn my attention to some fragmentary specimens in his collection, which are without doubt portions of a Pterygotus, probably of some size, judging from the size of the fragments. These he has kindly permitted me to exhibit, and offer the following remarks on. The first specimen is only a fragment of some part of the exoskeleton, but on one of the edges is visible the characteristic semicircular plicae which is the common ornament of the genus. The second specimen is likewise a fragment, but is of interest, because it shows a punctate