Freeman et al.—Upper Cambrian linguliform Brachiopods from Texas
hemispherical pits ~3 μm in diameter interspersed with clusters of smaller pits <1 μm in diameter. An internal pedicle tube is present, but other features of the ventral interior are exfoliated or obscured by matrix. Gently convex dorsal valve, transversely suboval in outline.
Larval shell with margin thickened and prominent (Fig. 4.8). Gently anacline pseudointerarea divided by wide, shallow, triangular median groove. Median buttress well developed, transversely rectangular in outline. Low median ridge arises just anterior of median buttress and extends to a position well to the anterior ofmedian point of valve length (Fig. 4.13, 4.14).Median ridge rounded along ventral margin. Suboval cardinal muscle scars large and prominent, closely spaced.
Materials.—Sixty dorsal valves, 28 ventral valves, and one whole shell (Supplemental Data Table 2), including illustrated dorsal valves NPL 45474 and NPL 45476 and ventral valve NPL 45475.
Remarks.—The material is badly exfoliated and mostly frag- mental. Pseudointerareas of the ventral valves have either a weak intertrough (Fig. 4.10–4.12) or are undivided—a feature common to many species of Eurytreta. Interior features of both valves are poorly known due to exfoliation. The low median ridge of the dorsal valve is similar to
stratigraphically lower specimens assigned herein to Eurytreta sublata?, but the ventral valves differ in having an indistinct intertrough rather than an interridge. In Utah the species Eurytreta cf. bisecta (Matthew, 1901) replaces Eurytreta sublata in the lower part of the Cordylodus lindstromi conodont Zone (Popov et al., 2002), but this Texas material is not assignable to E. cf. E. bisecta, which has an angular tip on the dorsal median ridge. Popov et al. (2002) described specimens of Eurytreta sublata from the Cordylodus proavus Zone as more commonly having an interridge than stratigraphically higher specimens that were more commonly undivided. The lower Texas Eurytreta specimens assigned to E. sublata? herein are from the Cordylodus proavus Zone and the base of the overlying Cordylodus intermedius Zone, and it is possible that the stratigraphically higher specimens with an undivided ventral pseudointerea assigned to Eurytreta sp. 1 herein may be Eurytreta sublata instead. A low median ridge connected to the median buttress, a
thickened margin of the dorsal larval shell, and an indistinctly divided ventral pseudointerarea are characteristics of E. sabrinae (Callaway, 1877) as well (Streng et al., 2011). The Texas material is too poorly preserved to compare other diagnostic characters of the species, although the median ridge
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on the few unexfoliated dorsal valves (Fig. 4.13, 4.14) appears similar to E. sabrinae.
Genus Quadrisonia Rowell and Henderson, 1978 Type species.—QuadrisoniaminorRowell andHenderson, 1978.
Diagnosis.—As in Freeman and Miller (2011b). Quadrisonia lavadamensis Popov, Holmer, and Miller, 2002 Figure 4.15–4.25
2002 Quadrisonia? lavadamensis Popov, Holmer, and Miller, p. 225, fig. 8.1–8.9.
2011b Quadrisonia lavadamensis (Popov et al., 2002); Freeman and Miller, p. 59, fig. 9A–9O.
Holotype.—Dorsal valve (USNM 516760) from the Lava Dam Member of the Notch Peak Formation, western Utah (Popov et al., 2002, fig. 8.3).
Diagnosis.—As in Popov et al. (2002).
Occurrence.—In the Saukia trilobite Zone and the Proconodontus tenuiserratus and Proconodontus poster- ocostatus conodont zones, in the Point Peak Member and the San Saba Member of the Wilberns Formation. In the same conodont zones in the Hellnmaria Member of the Notch Peak Formation in Utah (Freeman and Miller, 2011b) and in the Proconodontus muelleri conodont Zone and the Eoconodontus notchpeakensis and Cambrooistodus minutus subzones of the Eoconodontus conodont Zone in the Red Tops Member and Lava Dam Member of the Notch Peak Formation in Utah (Popov et al., 2002; Miller et al., 2011).
Materials.—Sixty dorsal valves and 51 ventral valves (Supple- mental Data Table 1), including illustrated dorsal valves NPL 85573 and NPL 85574, and ventral valves NPL 85575 and NPL 85576.
Remarks.—Most specimens were too fragmental and abraded to measure accurately, but proportions of more complete speci- mens appear to be identical to the type material (Popov et al., 2002). The most complete valves are figured.
Order Siphonotretida Kuhn, 1949
Superfamily Siphonotretoidea Kutorga, 1848 Family Siphonotretidae Kutorga, 1848 Genus Schizambon Walcott, 1884
Figure 4. Eurytreta sublata? Popov, in Koneva and Popov, 1988 from the base of the Cordylodus intermedius conodont Zone and from the Symphysurina trilobite Zone, in the San Saba Member of the Wilberns Formation, Texas; all are from sample TC-1460; scale bar is 300 μm(1, 2) and 500 μm(3, 6, 7): (1, 2) ventral valve exterior and oblique exterior (NPL 45471); (3–5) dorsal valve exterior, detail of larval shell, and detail of micrornament on larval shell at location indicated by arrow on (4) (NPL 45472); (6, 7) dorsal valve interior, oblique view of dorsal interior (NPL 45473). Eurytreta sp. 1, from the Cordylodus angulatus conodont Zone, in the lowest part of the Threadgill Member of the Tanyard Formation, Texas; all are from sample LR-1465.5 Scale bar is 300 μm(8, 10–12) and 500 μm(13, 14): (8, 9) dorsal valve exterior, detail of microornament on larval shell at position indicated by arrow on 8 (NPL 45474); (10–12) ventral valve oblique lateral view, oblique exterior, and oblique posterior view, NPL 45475; (13, 14) dorsal valve oblique interior, interior, (NPL 45476). Quadrisonia lavadamensis Popov, Holmer, and Miller, 2002, from TC-1160 in the Proconodontus tenuiserratus conodont Zone, in the Point Peak Member of the Wilberns Formation, Texas: scale bar is 300 μm(15–17, 20), 500 μm for all others unless indicated otherwise: (15–19) ventral valve exterior, oblique view of exterior, posterior view, detail of larval shell ornament at location indicated by arrow on (15), detail of larval shell and intertrough (NPL 85573); (20–22) dorsal valve exterior, detail of larval shell ornament at location indicated by arrow on 20, detail of larval shell and postlarval shell drapery-like ornament (NPL 85574); (23) ventral valve fragment interior (NPL 85575); (24, 25) dorsal valve interior, oblique view of dorsal valve interior (NPL 85576).
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