NEW PARABLASTOIDS FROM THE WESTERN UNITED STATES

Abstract

Two new genera and two new species of Parablastoidea are described from Early and Middle Ordovician faunas from the western United States. Eurekablastus n. gen. is similar in plating to Blastoidocrinus except that it possesses a conical pelvis with shallow basal cavity restricted to the basal circlet, one to two additional plate sets above the radials, medium to long cataspire slits, and lacks oral and ambulacral crests. Eurekablastus ninemilensis n. sp. from the Lower Ordovician Nimemile Shale of central Nevada and Eurekablastus rozhnovi n. sp. from the Lower Ordovician Wah Wah Limestone and uppermost Fillmore Formation of western Utah differ in thecal proportions, the number and distribution of interbrachial plates, the relative proportions of bibrachials and radials, and the length of the cataspire slits. Parabolablastus n. gen. is erected for Blastoidocrinus?? elongatus (Sprinkle), 1973, based on a mostly complete but crushed theca from the lower Middle Ordovician Antelope Valley Limestone of central Nevada. The plating in Parabolablastus may have been derived from Eurekablastus, but differs by having large parabolic deltoid plates, greatly enlarged bibrachials that form a complete circlet at the top of the pelvis and extend up into the vault interrays, and fewer or smaller plates in the lower pelvis. Blastoidocrinus? rossi Sprinkle, 1973, and B.? nevadensis Sprinkle, 1973, remain questionably assigned to Blastoidocrinus because they appear to have a high, fused, conical or cylindrical oral crest unlike the peristomial cover plates found in Eurekablastus and probably Parabolablastus.