28


Journal of Paleontology 90(1):10–30


Parahio River, Spiti region, Parahio Formation, informal global Stage 5 of the Cambrian. Five specimens available.


Spines indet. Figure 12.1–12.10 Material.—WIMF/A/3996-4003.


Description.—All three morphotypes display long, thin, spines tapering toward apex, circular to elliptical in cross section and protruding from a variably shaped base. Spines are bilaterally symmetrical about medial plane, and taper rapidly near the base, becoming less tapered towards apex, which is not preserved. In one morphotype the base is hemispherical in plane view, and concave in profile. Specimens apparently have pores on their outer surface, with all pores having a similar size of approximately 10 µm, a similar circular shape, and appear to be equally distributed across the surface of the base at a distance of approximately 20–30 µm. Base of second morphotype subcircular to oval when viewed from above, with the spine protruding from the center of the base. Third morphotype has a thin elliptical base when viewed from above and is convex when viewed laterally.


Remarks.—The first morphotype is superficially similar to an eodiscid meraspid pygidium, as illustrated in Zhang and Clarkson, (2012, pl. 18, fig. 6, 8, 10, 16, 18), with a straight margin on one side confluent with curved opposite margin. However, the spine extends from the base towards the straight margin, not towards the curved margin, and there is no articulating facet. The second morphotype has a similar


morphology to Archaeopetasus exavatus (Bengtson et al., 1990, fig. 106 A–E), but those spines appear to have a variable length unlike the specimens described herein. Lee (2008, fig. 5.3, pg. 1157) imaged a spinous specimen with a similar morphology to the third morphotype described herein (Figs. 12.6–12.10) as an indeterminate trilobite spine that was presumably axial. Other microfossil material illustrated from the Parahio Formation that might include trilobite fragments is some or all of that attributed to “Helkiaria” by Singh et al. (2015, p. 2194, figs. 3.20–3.24). This new generic name is a nomen dubium, being unac- companied by a description. Perhaps the authors intended to refer to this material as halkieriid, a suggestion supported by the spelling that they gave on pg. 2193 of their paper.


Occurrence.—New material from Parahio Formation carbonates collected at 775.41m (PO24) and 776m (PO25) (both Paramecephalus defossus Zone) above the base of the Parahio Valley section on the north side of the Parahio River, Spiti region, Parahio Formation. Approximately 15 specimens available.


Acknowledgments


We thank Dr. S.K. Parcha and the Wada Institute of Himalayan Geology for assistance in the field, and for providing the repository for the figured material, and Dr. B.R. Hunda of the Cincinnati Museum Center for housing residual material. Mr. P. Sarkar and repository division of the Geological Survey of India, Kolkata, kindly allowed inspection of previously


figured material, and we extend thanks to Dr. D. Mukherjee of that institution. S. Wernette kindly performed the EDS analysis. Drs. M.L. Droser, P.D. Kruse, L. Laibal, J.F. Miller, J.L. Moore, L.E. Popov, A.W.A. Rushton, and P.M. Sadler all provided helpful advice during the study. Drs. P.D. Kruse, M. Martí Mus, and C.B. Skovsted provided thoughtful reviews of the manuscript and S. Wernette did the EDS analysis. This work was supported by National Science Foundation grants EAR-9980426 and EAR-1124303 to N.C.H.


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