A Triassic crinoid from Mexico

A new genus and species of the Roveacrinidae is described from the Upper Triassic-of Mexico. The species is based on a large collection of free centrodorsal, radial, and brachial plates. CRINOID remains from the Triassic are rare. Only six species, based on columnals and referred to the genera Isocrinus and Encrinus have been described from North America (Biese, 1934, and SievertsDoreck and Biese, 1939). Swimming and pelagic crinoids are unknown from the Triassic, the earliest records of this type. occurring in rocks of Jurassic age. In February of 1947, Dr. J. B. Reeside, Jr. of the United States Geological Survey sent the writer hundreds of associated centrodorsal, radial, and brachial plates from the Upper Triassic (Karnic) of Sonora, Mexico. These Triassic crinoids bear a marked resemblance to those from the Cretaceous of Europe and North America included in Roveacrinidae (Peck, 1943). The brachials are almost identical in construction with those described by Sieverts-Doreck (1932) from the Cretaceous of Germany. The Triassic forms lack the ornamentation possessed by the Cretaceous representatives of the Roveacrinidae, and the radials were easily separated from the centrodorsals on fossilization and occur as free plates. Another unusual character of the Triassic forms is that the radials were not in contact proximally. Roveacrinidae have been previously recorded from the Cretaceous of England and Germany, and from the Lower Cretaceous of Texas. This record extends the range of the family from the Upper Triassic to Cretaceous. These small crinoids are probably widespread and of frequent occurrence. They undoubtedly have been noted by many investigators and identified as echinoderm fragments. The Roveacrinidae had been noted by several investigators in the Lower Cretaceous of Texas but consistently misidentified (Peck, 1943). Burck81 hardt (p. 6, 1930) listed bryozoa from the locality from which these Triassic crinoids were collected, but Reeside states (letter) We found no Bryozoa in a very large and varied collection from this locality. On casual examination the coarsely porous surfaces of many of the plates, especially the centrodorsals, closely resemble the surfaces of finely branching Bryozoa. The writer believes that the Roveacrinidae will be found in many formations of the Mesozoic and that the pelagic habits and easily recognizable characters will make them valuable stratigraphic fossils. Mrs. Vaona Hedrick Peck retouched the photographs, made the restoration drawing, and arranged the photographs on Plate 20. The retouched photographs are as accurate as it is possible to make them. With the exception of the outline drawing, no restorations or interpretations have been made. The holotype, all figured specimens, and the bulk of the material on which this paper is based, are deposited in the U. S. National Museum. A set of paratypes is deposited in the University of Missouri Collections. Family ROVEACRINIDAE Peck, 1943, emend. Small, stemless, pelagic Articulata with coarsely porous calyces composed of five radial plates and noncirriferous centrodorsals. Sides of adjoining radials extended distally to form prominent processes between the arm facets. Arms ten, the division on the second brachial. Brachials joined by alternating muscular articulations and cryptosynarthial unions to SBrBr4, and probably beyond. All brachials except PBrBri and SBrBri possess strong, distally projecting serrated processes bordering the ventral furrows. This content downloaded from 207.46.13.64 on Mon, 04 Jul 2016 05:44:51 UTC All use subject to http://about.jstor.org/terms