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Helotholus praevema Weaver, 1983

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Shell consists of two segments. Cephalis spherical, with numerous circular to subcircular pores and 1 or 2 apical spines. Cephalis width, one-half to two-thirds thorax. Collar stricture is distinct. Thorax variable, predominantly subcylindrical, sometimes cup-shaped, with numerous circular to elliptical pores. Commonly pores are irregularly spaced or exhibit crude longitudinal alignment. In well-preserved specimens, supplementary spines protrude from thoracic wall as apparent extensions of the internal structure. Internal structure consists of the elements A, D, V, Lr and L1 spines, all arising from a common point in plane of collor stricture. An axial spine (Ax) projects downward into thoracic cavity from this point. No distinct median bar (Mb) observed; point of convergence of internal spines could be preceived as short Mb. Where primary interval spines are fused to thoracic wall, it is drawn into shell, forming grooves on surface.
Weaver 1983











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