Post-extinction survivor fauna from the lowermost Famennian of eastern North America Author Day, Jed Author Over, D. Jeffrey text Acta Palaeontologica Polonica 2002 2002-12-31 47 2 189 202 journal article 300554 10.5281/zenodo.13174914 c2009942-e0f2-4d16-b1ef-026cefdf1680 1732-2421 13174914 Retichonetes aff. S. obscurus Cooper and Dutro, 1982 Fig. 4A–D . Retichonetes obscurus ; Cooper and Dutro 1982: 58 , pl. 11: 19–25. Material .—Figured specimens NYSM 15704, NYSM 15705, NYSM 15718; unfigured specimens NYSM 15708, NYSM 15709, and NYSM 15710; and approximately 2,000 unnumbered complete and partial shells on surfaces of parts and counterparts of split slabs. Remarks .—This small chonetid ( 4–8 mm in width) is the numerically dominant species in the fauna of the Hanover shell bed. This form was initially interpreted as a new genus by Day (1997) . However, careful study of numerous specimens indicates that the chonetid in the Hanover Shale shell bed is a species of Retichonetes Muir−Wood (1962) close to R. obscurus Cooper and Dutro (1982) described from the Ready Pay and Box members of the Percha Formation of southern New Mexico . Cooper and Dutro (1982 : fig. 7) show the Percha as possibly spanning the interval of the Upper Pa. crepida Zone to Po. styriacus Zone (lower–upper Famennian). The Po. styriacus Zone as shown in fig. 7 of Cooper and Dutro (1982) is equivalent to the Lower and Upper Pa. postera and Lower Pa. expansa zones of the current Famennian conodont zonation (see revisions by Ziegler and Sandberg 1984: 183–184 , figs. 1–4). Retichonetes obscurus from New Mexico is similar to the Hanover specimens in overall shape and size and numbers of costellae. The Hanover form differs by the presence of well preserved concentric growth lines on the rounded costellae and in the interspaces, and having a better developed dorsal septum than that shown for R. obscurus ( Cooper and Dutro 1982 : pl. 11: 24). Another similar form Retichonetes sp. is illustrated by Schwimmer and Feldmann (1991: figs. 7.1–7.8) from the Famennian Chagrin Shale of northeast Ohio . Their shells are similar to the Hanover material in overall shape, size, and in the high angle (60 to 90°) that the oblique orthomorph spines arise from the posterior margin of the ventral valve. They do not mention the reticulated ornament typical of species of Retichonetes ( Muir−Wood 1965 : H428, fig. 286). Reticulated ornament is seen on shells of R . aff. R. obscurus with well preserved shell material, produced where fine concentric growth lines cross the radial costellae. Spines along the ventral cardinal margins in both the Hanover specimens and R . sp. from the Chagrin Shale of Ohio (Schwimmer and Feldmann 1991) arise at high angles as is typical for the genus (see Muir−Wood 1962: 62 , 1965 : figs. 285, 286).