NEW CAMERATE CRINOID FROM THE LATE ORDOVICIAN (SANDBIAN) BROMIDE FORMATION, ARBUCKLE MOUNTAINS, SOUTHERN OKLAHOMA

The Bromide Formation has produced one of the largest Ordovician echinoderm faunas ever collected from North America, now including over 12,000 specimens assigned to 62 genera and 12 classes. This echinoderm fauna was monographed in 1982, but additional examples of rare taxa, described from one or a few specimens, or entirely new taxa have gradually accumulated over the past 33 years.

Camerate crinoids are an especially diverse group in the Bromide, with 13 genera occurring in all three of the rich echinoderm zones, including two cleiocrinid, one reteocrinid, one anthracocrinid, and six rhodocrinitid diplobathrid camerates, along with two glyptocrinitid and one colpodecrinid monobathrid camerates. Recently, another apparently new rhodocrinitid camerate has been discovered in the Upper Echinoderm Zone at two localities in the northern Arbuckles. This new camerate is represented by a large, well-preserved, calyx and seven, small-to medium-sized, less-complete cups or calyces. Medium-to-large calyces have a cauldron shape with a relatively deep basal cavity; subdued ridges around the basal circlet leading to subdued ray ridges, but no CD ray ridge; two primibrachs, two secundibrachs, and many tertibrachs leading to 20 arms branching off around the summit; relatively few, large, interradial and interbrachial plates; and a slightly domed tegmen with small pustular plates and a low anal vent. Arm bases have cuneate to biserial brachials and are separated by 4-5 fixed pinnules. The proximal stem is round, fairly large, and has a pentagonal lumen.

These features resemble the Bromide rhodocrinitids Paradiabolocrinus stellatus, also found in the Upper Echinoderm Zone at one of these localities, and Crinerocrinus parvicostatus, known from a single incomplete cup at a Pooleville locality in the Criner Hills. The first species has a much smaller, bowl-shaped calyx, a shallower, conical, basal cavity, more highly ornamented basal and ray ridges plus a CD ray ridge, numerous, smaller, interbrachial plates, and only 10 arms branching off the summit with gaps between the rays. The second species has a larger bowl-shaped cup, a wider, conical, basal cavity with infrabasals visible, very thin ray ridges, wider interrays with more interbrachials, and no tegmen, but is the only other Bromide rhodocrinitid inferred to have 20 arms.