Chapter Seven. Notes on and Description of Oleneothyris fragilis (Morton) 1828 (Brachiopoda, Terebratulidae)

The Oleneothyris biostrome, a well-known stratigraphic marker at the top of the Hornerstown Formation in the Atlantic Coastal Plain, contains two distinct species of a large terebratulid brachiopod. These two species, 0. harlani (Morton) and 0. fragilis (Morton), may be differentiated by the prominent sulcus and fold, along with two pronounced dorsal ridges on the less robust 0. fragilis. The latter species is confined vertically to a lens within the biostrome and geographically to the area around New Egypt, New Jersey. A narrowly triangular, strongly arched loop, characteristically terebratulid, is found to differ slightly from that of 0. harlani. Since the holotype of 0. fragilis, first described in 1828 by S. G. Morton, is either no longer in existence or lost, a neotype (RU 5700) is herein designated. The neotype is housed in the Rutgers University Geological Museum, New Brunswick, New Jersey.