A new Tolypelepidid (Agnatha, Heterostraci) from the Late Silurian of Poland Marek Dec Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818, Warsaw, Poland 〈mdec@twarda.pan.pl〉 Abstract.—Tolypelepis mielnikensis n. sp. from a core sample of the Late Silurian (Pridoli) succession in Mielnik, Poland shares tolypelepidid features such as a subdivision of the dorsal shield into epitega, and ornamentation of short dentine ridges grouped into scale-like units with a coarser, higher median ridge encircled by narrower and lower ridges. A constriction of the dorsal shield anterior to the orbit level with the orbital notches significantly deeper than in other tolypelepidids discriminates it from other Tolypelepis species. Introduction The genus Tolypelepis was monotypic over for 120 years, the only species included being T. undulata. The original description by Pander (1856) was based on a small shield fragment from the Ohesaare Cliff (Estonia), which was Pridoli in age. Schmidt (1893) introduced the new name Tolypaspis for a well-preserved dorsal shield of the same species. A more detailed description of Tolypaspis undulata, published by Rohon (1893) was based on the material from the same locality (Saarema Island, Ohesaare Cliff). All the above mentioned material belongs to the same genus Tolypelepis, now considered valid due to clari fication by many subsequent authors (Rohon, 1893; Hoppe, 1931; Kiaer, 1932). Other materials assigned to Tolypelepis undulata by these authors have mainly been obtained from the same locality and strata (Ohesaare Cliff, Pridoli Series, upper Silurian, Mark-Kurik, 1969; Mark-Kurik and Noppel, 1970). Märss (1977) described all the material of Tolypelepis undulata. The new material that she described and figured came from the same strata of Ohesaare Cliff and Ruhnu drill core in Estonia. Dineley and Loeffler (1976) reported a new species of Tolypelepis, T. lenzi, from the upper Silurian of northern Canada (Mackenzie Mountains). They also established a new genus, Asketaspis, related to Tolypelepis (Dineley and Loeffler, 1976), from the same upper Silurian strata. This decision supports the monophyletic suprageneric taxon, Tolypelepidinae, first used by Denison (1964), nested in Heterostraci. Tolypelepis material was also described by Loeffler and Jones (1977) from Arctic Canada (Somerset Island), and assigned to a new species Tolypelepis leopoldensis and to T. cf. leopoldensis. Recently, a complete, articulated specimen of a putative tolypelepidid, Athenaegis chatterton, has been described from Wenlock, lower Silurian beds, Mackenzie Mountains (Soehn and Wilson, 1990). Material and geological setting Two associated specimens (ZPAL Ag–II/1–2), described herein, were collected by Henryk Tomczyk (Institute of Geology, Warsaw) from one core sample from a borehole at Mielnik eastern Poland (Fig. 1). The deep boring was designed by the Polish Geological Institute and drilled in 1959. It penetrated the Late Silurian (Pridoli) succession and reached a depth of 1813.10 m in Precambrian rocks (Urbanek, 1997). The Precambrian basement is overlain by Ordovician and Silurian deposits, which are uncom- formably covered by Permian clastics. There is no precise analysis to ascertain how deep the Permian erosion was or how big was the stratigraphical gap that comprises the Devonian and Carboniferous, but also potentially includes the uppermost part of the Silurian strata. The Mielnik IG-1 drill core was almost complete, with a core diameter of 10–12 cm (Urbanek, 1997). The specimens ZPAL Ag–II/1–2 were collected from one bore-core sample from the Late Silurian (Pridoli) succession at a depth of 602.3–606.8 m (Fig. 1). According to Kozlowski and Sobień (2012), the succes- sion represents a periplatform setting of a neritic carbonate platform. The considerable thickness, along with the low-energy sedimentary environment and completeness of graptolite succession, suggest a continuous and nearly constant rate of sedimentation. The sample is accurately dated based on graptolites (Urbanek, 1997). The graptolites are numerous and well preserved, varying from flattened specimens to 3D preservation. The degree of graptolite compression is correlated with the clay content in the matrix because flattening most probably depends on the compac- tion of the initially loose silty sediments (Urbanek, 1997). A combination of 3D and flattened specimens are present within one sample. The agnathan remains were found about 30 m above the last occurrence of the graptolite Neocolonograptus lochko- vensis lochkovensis, at a depth of 634.15 m (Urbanek, 1997), which defines the lochkovensis graptolite Zone. The measurements of the shield of T. mielnikensis n. sp. from Mielnik follow those used by Denison (1964). Systematic palaeontology Class Pteraspidomorphi Goodrich, 1909 Subclass Heterostraci Lankester, 1868 Journal of Paleontology, 89(4), 2015, p. 637–644 Copyright © 2015, The Paleontological Society 0022-3360/15/0088-0906 doi: 101017/jpa.2015.28 637