Harrell L. Strimple

Sciadiocrinus, convergence on the family Pirasocrinidae (Crinoidea: Echinodermata)

Sciadiocrinus Moore and Plummer is synonymized with Schistocrinus Moore and Plummer, with the name Sciadiocrinus retained by the Law of Priority. This synonymy is based on a reexamination of the type material, study of a previously undescribed ontogenetic sequence in S. tegillum Strimple and Moore, and close inspection of separate radial plates and anal-sac spines. The holotype specimen of the type species of Sciadiocrinus was incorrectly illustrated in the original description of the genus, and appears to be immature. The basal plates of this specimen are shown to be separated from each other by the junction of the radial plates with the infrabasals—a principal character in the original concept of Schistocrinus. The Sciadiocrinus tegillum hypodigm now includes specimens which also have relatively large radial–infrabasal sutures as well as individuals with little or no contact between these plates. Examination of this collection and previously described material shows that mode of arm branching, details of radial-plate articular facets, and some features of the anal-sac spines are also equivalent in the two genera. Sciadiocrinus , presently classified in the family Pirasocrinidae, is distinct from all known pirasocrinid taxa in a number of morphological characters. We believe the genus should be removed from the Pirasocrinidae, and recommend its assignment to the family Anobasicrinidae based primarily on similarities in arm structure. The remarkable convergence between Sciadiocrinus and the Pirasocrinidae emphasizes the adaptive significance of the spinose, umbrella-like anal-sac roof, which apparently served as a deterrent to predators.

ABNORMALITIES IN PENTREMITES SAY (BLASTOIDEA) FROM THE PELLA FORMATION (UPPER MISSISSIPPIAN) OF IOWA

Approximately 10,000 determinable specimens of Pentremites pulchellus Ulrich (Blas- toidea, Echinodermata) from a single quarry in the Pella Formation near Oskaloosa, Mahaska County, Iowa, have been examined for abnormal morphologic characters. The total frequency (2.7%) and the frequency among different types of abnormalities (ambulacral 29%; basal 46%; symmetrical 12%) are significantly different in the Pella material than in previously published studies (Wanner, 1932; Macurda, 1980). The greater frequency of abnormalities in the Pella For- mation than in previous studies may reflect higher environmental stress because of variable tem- peratures or salinities or both. The kinds of abnormalities are the same among published studies, which suggest that the underlying biological causes of abnormalities were similar throughout the geologic history of the blastoids. Ambulacral abnormalities are symmetrically distributed, but the division and inversion of basal plates show an asymmetrical distribution as previously recorded by Macurda (1980). The Pella Formation is of Genevievian age (Upper Mississippian) based on the occurrence of Pugnoides ottumwa (White) and convex ambulacra in Pentremites pulchellus. Other unequivocal guide fossils are unknown in the Pella Formation.

Mooreocrinus and Ureocrinus gen. nov., with Notes on the family Cromyocrinidae

A new echinoderm genus, Mooreocrinus, is proposed to embrace those forms of Cromyocrinus having more than five arms. Species of Carboniferous age from Russia, Scotland and the United States are referred to it. Another new genus, Ureocrinus, is proposed to embrace Permian and Carboniferous cromyocrinids from Great Britain, Scotland, Russia, India, Timor, and the United States possessing five arms and variations in anal area and shape of cups from the ten-armed genus Ulacrinus.

A microcrinoid colony from a cephalopod body chamber (Chesterian; Arkansas)

An unusual occurrence of a colony of microcrinoids from shale within a fragment of a large orthoconic nautiloid body chamber is described from the Imo Formation (Mississippian, Chesterian) near Elba, Arkansas. The colony, about 70 individuals, consists principally of immature specimens that lack facets for the arms, and a few mature specimens with four or five arm facets. The crinoids are interpreted as record of a census population that was engulfed suddenly by mud. The crinoids are assigned to Allagecrinus coronarius Gutschick, 1968. The body chamber may have been broken during predation by other large cephalopods, or sharks, known from the Imo, or by post-mortem transport. The shell served as a firm substrate on which the microcrinoid larvae could settle and the convex sides may have provided some protection from currents.

The inadunate crinoid genus Cryphiocrinus Kirk

Cryphiocrinus Kirk is a genus which may possess a delicate stem, or may lose the stem as an adult, making it essentially eleutherozoic. C. girtyi Kirk, type species, is documented with certainty from Chesterian rocks of Oklahoma and Arkansas for the first time. C. rotundus Kirk is reported from the Renault Formation of Illinois and a possible occurrence in the Pride Mountain Formation of Alabama is noted. The genus has previously been recognized in Chesterian, Upper Mississippian, (Lower Carboniferous), strata exposed in West Virginia, Kentucky and Oklahoma, U.S.A. Possible affinity with Hosieocrinus Wright from the Lower Limestone Group (Visean) in Scotland is discussed.

Peremistocrinus from the Dewey Limestone Formation, Oklahoma

The first systematic study of anal variations found among various Carboniferous crinoids was presented by James Wright ( Geol. Mag. , lxiii, 1926) and covered Eupachycrinus calyx (McCoy) (now Phanocrinus Kirk) and Zeacrinus konincki Bather. Subsequently ( Geol. Mag. , lxiv, 1927), the genus Hydreionocrinus , and Ulocrinus globitlaris (Geinitz) (now Ureocrinus Wright and Strimple, Geol. Mag. , lxxxii, 1945) were also considered. A total of 2,014 dorsal cups from the Scottish Lower Carboniferous (Mississippian) were involved in the examinations. These specimens were all from strata considered equivalent to the Chester Series (upper Mississippian) of North America. When presenting the genus Phanocrinus Kirk ( Journ. Paleont. , 11, 1937) recognized the importance of Wrights studies, but noted that examination of an almost equal amount of American material (primarily the Springer collection of the U.S. National Museum) had failed to disclose such great variations. That Kirk was highly impressed by Wrights studies is certain, for in personal conversations, several years ago, he emphasized the potentialities as they might affect my impending studies of Pennsylvanian crinoids. It has, therefore, been with much interest that I have watched similar patterns of development appearing in the large collections being made from both Chester (Upper Mississippian = European upper Lower Carboniferous) and Missouri (Middle Pennsylvanian = European middle Upper Carboniferous) of north-eastern Oklahoma.