The fauna described in this paper was collected from a shale quarry (locally known as the ‘Shale Bank’) on the grounds of Mohonk Mountain House in the lower Hudson Valley, New Paltz, New York. Here we describe the crinoids of the Upper Ordovician (approximately 450 million years old) Martinsburg Formation. The Martinsburg consists of a medium dark-gray shale interbedded with sandstone beds that show graded bedding and cross laminae. The fauna includes a new species of Pycnocrinus, as well as the long-stemmed, small-crowned inadunate crinoids Ectenocrinus, Cincinnaticrinus, and Merocrinus, which are also present in several other Late Ordovician offshore faunas. The modes of life of the crinoids are reconstructed, based particularly on stem lengths and aspects of feeding related to the density of branching in the crinoids’ arms. This fossil occurrence probably represents a relatively low energy, offshore mud bottom environment that was episodically stirred by storm waves and currents.

A new crinoid fauna has been discovered in the Upper Ordovician (Katian) Martinsburg Formation at a small shale quarry, locally known as the ‘Shale Bank,’ on the Shawangunk Ridge in Ulster County, NY. The assemblage, which is from a relatively low energy, offshore mud-bottom environment, includes four identified species, including a new species of glyptocrinid camerate, Pycnocrinus mohonkensis n. sp., described herein. Crinoid taxa in order of increasing branch density in the assemblage include (1) the dicyclic inadunate Merocrinus curtus with irregularly isotomous and heterotomous, non-pinnulate arms and a stout cylindrical column exceeding 700 mm; (2) the disparids Cincinnaticrinus varibrachialus, with heterotomous non pinnulate arms, and Ectenocrinus simplex, with extensively branched ramulate arms and meric columns of 460–500 mm; and (3) the camerate Pycnocrinus mohonkensis n. sp., with uniserial pinnulate arms and a somewhat shorter column. Some cylindrical stems with nodose and holomeric columnals are thought to belong to unknown camerate crinoids with pinnulate arms. Filtration theory is used to model food capture in the Martinsburg crinoids. Surprisingly, even densely pinnulate camerates were able to survive in this setting, suggesting that ambient currents attained velocities exceeding 25 cm/sec even in this offshore setting. Similar assemblages were widespread in eastern Laurentia during the Late Ordovician.