858
Journal of Paleontology 92(5):850–871
sixth to ninth secundibrachial; tertaxil from ninth to fourteenth tertibrachial. Tertibrachials as high as wide or higher than wide. Column xenomorphic, pentalobate, pentameric; column
index N212. Proxistele with columnals slightly heteromorphic, pentameric or cryptic pentameric; parallel sided; nodals twice as wide as high with ratio higher for internodals; N212 columnal organization present but subtle. Mesistele columnals crypto- pentameric or holomeric; nodals approximately two times as wide as high, latus very convex; mesistele first internodals three times wider than high, latus very convex; mesistele tertinterno- dals 1.6 times as wide as high, straight-sided. Dististele columnals homeomorphic, pentameric. One juvenile specimen with nearly complete column ending in coil; one larger specimen with distal tip abutting against much larger columnal at high angle (thus consistent with but not definitive of distal coil in adult). Aspects of columnal facets unknown.
Materials.—CMC IP 36696, 69219, and 74961; UMMP 74658 − 74660.
Measurements.—UMMP 74658: CrH, 30.0*; ACH, 5.4; ACW, 5.4; CoH, 60.0*. UMMP 74659: CrH, 15.0*; ACH, 2.7; ACW, 3.4*; CoH, 60.0*.UMMP74660: CrH, 17.0*; ACH, 5.9; ACW, 4.6; CoH, 11.0*.
Remarks.—As with Daedalocrinus bellevillensis, the calcite skeleton of Isotomocrinus tenuis can be preserved with a very dark coloration (Fig. 4.4). Further, as in D. bellevillensis, this occurs most commonly on the aboral cup plates, but on some specimens, the coloration can extend onto the column or onto the proximal brachials. Isotomocrinus tenuis is a relatively common species from
the Brechin Lagerstätte, including both juveniles and adults. The shape of the aboral cup changes through ontogeny with the cup ~1.25 times higher than wide in subadult specimens and more equidimensional in adults.
Family Anomalocrinidae Wachsmuth and Springer, 1886
Remarks.—Anomalocrinus is aptly named. The upper Bobcaygeon-lower Verulam interval in Ontario contains numerous specimens of a species that should be assigned to Anomalocrinus and Glaucocrinus falconeri? Parks and Alcock, 1912, which also could be assignable to Anomalocrinus. The original understanding for both Anomalocrinus and Glaucocri- nus Parks and Alcock, 1912 was confused by aberrant speci- mens. In the holotype of A. incurvus Meek and Worthen, 1865, the position of a D radial plate is occupied by two plates sepa- rated by a central, vertical suture. Many specimens of A. incurvus are known now, and the vertical suture is absent on other specimens, making the holotype presumably an aberrant morphology. The holotype of G. falconeri has only three free arms. The C and E radial plates lack an arm (Guensburg, 1992). As suggested by Guensburg (1992), the holotype of G. falconeri is undoubtedly also an aberrant specimen. Guensburg (1992) clarified the morphology of G. falconeri, including the presence of only three arms; and otherwise demonstrated that the recon- struction by Parks and Alcock (1912) and by Moore and Lane (1978b) did not represent the morphology of this taxon.
Remarks.—Although beyond the scope of the present investi- gation, it should be noted that the previously named species of Anomalocrinus are in need of reevaluation. Specimens of Anomalocrinus are relatively large with relatively thin calyx plates; thus, specimens are easily compacted and disarticulated. This could explain the relative paucity of Anomalocrinus crowns preserved relative to, at least locally, the abundance of the distinctive Anomalocrinus holdfasts (Brett et al., 2008). Although specimens are available in museums, very few crowns of A. incurvus have been illustrated previously. It is probable that the holotype of A. incurvus is, as noted above, an aberrant specimen, and A. caponiformis is only known from a theca. Further, ?A. antiquus is a very small specimen and is known only from the aboral cup and proximalmost arms. As presently understood, species of Anomalocrinus are
diagnosed by the following characters: attitude of the radial circlet, the general character of the arms, character of the C-ray and E-ray primibrachials, shape of brachials, position of the primaxil, position of secundaxil, and arm branching. Anomalocrinus astrictus n. sp. has a more vertically directed radial circlet; brachials higher than wide, C- and E-ray
Guensburg, 1992, fig. 2) with the new Anomalocrinus material from the Brechin Lagerstätte supports the suggestion of Guensburg (1992) that Glaucocrinus is probably a junior synonym of Anomalocrinus and that the holotype and only known specimen of G. falconeri is an aberrant specimen. However, critical features needed to diagnose the species of Anomalocrinus (shape of the aboral cup, nature of brachials, and arm branching in the C and E rays) are not preserved on the holotype of G. falconeri, precluding comparison with other species of Anomalocrinus. Therefore, both G. falconeri and its monospecific genus Glaucocrinus are unrecognizable because of poor preservation and the fact that the holotype and only specimen is an aberrant individual. Thus, we designate Glaucocrinus and G. falconeri as nomina dubia. With the reassignment of Geraocrinus Ulrich, 1925 to the Columbicri- nidae (see Ausich, 1998), and the designation of Glaucocrinus as a nomen dubium, the Anomalocrinidae is monogeneric.
Genus Anomalocrinus Meek and Worthen, 1865
Type species.—Heterocrinus? (Anomalocrinus) incurvus Meek and Worthen, 1865, by monotypy.
Other species.—?A. antiquus Guensburg, 1984; A. caponiformis (Lyon, 1869); A. astrictus n. sp.
Occurrence.—Ordovician (questionably Sandbian), Tennessee, USA; (Katian), Indiana, Ohio, and Tennessee, USA, and Ontario, Canada.
Guensburg (1992) also demonstrated that the arms are only partially preserved, and the aboral cup is compressed. Guensburg acknowledged that Glaucocrinus could be a junior synonym of Anomalocrinus, but with only the holotype avail- able for study, Guensburg (1992, p. 6) concluded “I prefer to retain the status quo for the present; however, Glaucocrinus and Anomalocrinus are clearly closely related taxa.” Comparison of the holotype of Glaucocrinus falconeri (see
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