A review of SaltereIla (Phylum Agmata) from the Lower Cambrian in Greenland and Mexico

Records of SalterelIa from the Lower Cambrian in Greenland are reviewed and all specimens are referred to S. maccullochi (Murchison, 1859). Examples are iIIustrated for the first time from the Brønlund Fjord Group of Peary Land, central North Greenland and from the Hyolithus Creek Formation at Kap Weber and at C. H. Ostenfeld Nunatak, northern East Greenland. S. mexicana Lochman in Cooper et al., 1952, from Sonora, Mexico, is iIIustrated in thin sections and is placed into synonymy with S. maccullochi.

This brief review of the distribution and nomenclature of the genus SaltereIla Billings, 1861 in Greenland was prompted by the recent re-description by Yochelson (in press) of Salterella maccullochi (Murchison, 1859) from the Northwest Highlands of Scotland. S. maccullochi is the earliest described species currently assigned to Salterella and it is considered by Yochelson to be a senior subjective synonym of S. rugosa Billings, 1861, the type and best known species of the genus. The recognition of this synonymy necessitates re-assignment of Greenland specimens from S. rugosa to S. maccullochi.
SaltereIla was first described from North-West Greenland more than fifty years ago (Poulsen, 1927;1958; see Yochelson & Peel, 1980) and has been subsequently described from northern East Greenland (Poulsen, 1932;Griffin & Yochelson, 1975). Specimens are illustrated here for the first time from three additionallocalities in North and East Greenland; all are of Early Cambrian age.
The Greenland localities provide the northernmost record of Salterella on the present-day configuration of land and sea. During examination of collections from these localities, comparison has been made with the most southerly described specimens of Salterella, namely S. mexicana Lochman in Cooper et al., 1952, from Sonora, Mexico. It is our conclusion that S. mexicana is also a junior subjective synonym of S. maccullochi. The two records are of interest in view of their considerable geographic separation -more than 50 degrees of latitude or a distance in excess of 7000 km. Both outcrops probably occupied a broad Cambro-Ordovician outcrops in Bast Greenland are coloured black. equatorial belt in Cambrian time, but the unchanged position of Greenland relative to mainland North America from the Cambrian to the present day (Christie et al., 1981;Dawes & Kerr, 1982) maintains the separation.

Records of SalterelIa from Greenland
Salterella is now known from North-West Greenland, central North Greenland and northem East Greenland. Poulsen (1927Poulsen ( , 1958 described Salterella expansa and an indeterminate species of Salterella from the Wulff River Formation of late Early Cambrian age in Inglefield Land (figs 1, 2). Yochelson & Peel (1980) examined Poulsen's type specimens as well as new collections and considered S. expansa to be a junior subjective synonym of S. rugosa Billings, 1861, the type species of Salterella. Associated trilobites described by Poulsen (1927Poulsen ( , 1958 indicate the Bonnia-Olenellus Zone of the Early Cambrian. S. rugosa was also identified by Poulsen (1932) from the Ella Island Formation of Ella ø, northem East Greenland (figs 1, 2) and the specimens were subsequently examined by Griffin & Yochelson (1975). The associated fauna also includes olenellids and Bonnia (Cowie & Adams, 1957). in Peary Land (Ineson & Peel, 1980). No precise corre1ation is implied between the three sections.
Occurrences of S. maccullochi are starred. Troelsen (1956) recorded, but did not describe, SalterelIa from the basal Brønlund Fjord Dolomite of central southern Peary Land, central North Greenland ( fig. 1). The strata from which the samples were collected are now referred to member A of formation l of the Brønlund Fjord Group (Ineson & Peel, 1980). The identification was confirmed by Peel et al. (1974) on the basis of a few specimens in Troelsen's collections. The associated fauna is probably indicative of the Bonnia-Olenellus Zone (Palmer & Peel, 1979). In 1980, J. S. P. collected abundant specimens of SalterelIa from higher levels of the Brønlund Fjord Dolomite in strata now assigned to formation 6 of the Brønlund Fjord Group (Ineson & Peel, 1980; fig. 2 herein). These specimens are described and illustrated below ( fig. 5). The Salterella-yielding beds pass laterally into dolomites rich in archaeocyathaceans and overlie dark, silty dolomites with rich invertebrate faunas of Bonnia-Olenellus Zone age. Cowie & Adams (1957) . 1).
Haller's material is figured here for the first time ( fig. 4). The sequence exposed on C. H. Ostenfeld Nunatak contains the most northerly exposures of Cambrian and Ordovician strata in the East Greenland region (Frykman, 1979 Yochclson (in press) recently examined thin sections of specimens af SallerelJa maccutlochi (Murchison, 1859) from lhe Northwest Highbnds af ScotJand and concluded that tilis, the first dcscribcd species of Sairerella, is a senior subjcctive synonym of S. rugo.l'G Billings, 1861. The synonymy is eurrently extended to inc1ucte all presenlly known specimens uf Sa!rereifa from Greenland.

Description.
A full description of this species was given by Yochelson (in press). Descriptions and illustrations of S. rugosa were given by Yochelson (1977), Griffin & Yochelson (1975), and Yochelson & Peel (1980).  . 3). Details of the finer inner lamination and general structure of the conch are clearly visible. However, specimens showing breakage of the aperture and the apex are also present ( fig. 3D, E). In marked contrast, the specimens of S. maccullochi from the Hyolithus Creek Formation at C. H. Ostenfeld Nunatak are poorly preserved in dolomite. Features of the inner lamination and the apertural cavity are discernibie in the recrystallised carbonate, but the 'ghosts' visible in thin section are incomplete and often appear to lack the conch wall ( fig. 4). In this respect, they resemble Volborthella Schmidt, 1888, long considered to be a separate genus but now known to be based on specimens of Salterella from which the outer wall has been removed by erosion or solution (Yochelson, 1977;1981). The specimens of S. maccullochi from North Greenland ( fig. 5) are also preserved in dolomite. The matrix is an exceedingly tough, massive, paie huff grey dolomite which, in thin section, is seen to be weakly mottled. The conchs of S. maccullochi generally appear to be complete and outlines show well-preserved apices and apertural margins. However, the entire conch has recrystallised to spar and all detaiIs of internal structure have been lost ( fig.  5).
It has now proved possibie to examine thin sections of S. mexicana Lochman in Cooper et al., 1952 (fig. 6). The species has previously been iIlustrated from polished sections and external views but the thin sections have only recently become available. After study of the thin sections, it is our conclusion that S. mexicana is also a junior subjective synonym of S. maccullochi.