1010
Journal of Paleontology
Description.—Shell small to medium, average length of whole shells 12.2mm, width 15.4mm, thickness 9.8mm; transverse outline subpentagonal to subcircular; lateral profile dorsibiconvex. Shell ~81%as long aswide and ~65%as thick aswide. Astrophic hingeline approximately one-quarter to one-third shellwidth.Ribs strong and angular, simple, originating at the umbo; usually five to seven ribs on shell flanks, with four ribs in dorsal umbo and three ribs in ventral sulcus but occasionally more. Ventral umbo large and prominent with anacline interarea,
strongly incurved toward hingeline and projecting over the hinge in larger shells; triangular-shaped open delthyrium obscured by curvature of umbo. Triangular-shaped sulcus beginning within 2mm of ventral umbo, projecting upward to form prominent trapezoidal tongue at anterior commissure where it meets the dorsal fold. Dorsal umbo minute, interarea apsacline and minute with
obscured notothyrium. Dorsal fold beginning <1mm from dorsal umbo, triangular in outline, rising >1mm above shell surface in large shells, usually with flat and angular top but occasionally rounded near its margins. Teeth of moderate size supported by thin dental plates.
Dental cavities sometimes infilled by secondary shell material (as in Fig. 7). Ventral muscle scars obscured. Very small, ridge-like cardinal process. Dorsal median
ridge small, not connected to hinge plates. Sockets moderately deep, with hinge plates separated medially, lacking septalium.
Crura projecting anteriorly from crural bases embedded in shell material medial to sockets, becoming reduced in width anteriorly to become rod-like and eventually become lath-like and change orientation to a dorsal-ventral axis closest to the anterior. Dorsal adductor scars obscured.
Etymology.—Named after the Tarim region and paleoplate where the type material was collected.
Remarks.—Poor preservation of the material makes identifica- tion of fine details on the shell difficult. For example, Zhan and Li (1998) identified fine concentric filae in A. zhejiangensis from South China, but given the state of preservation of the current material, it is impossible to definitively determine whe- ther these shells possess this trait. The remnants of fine filae may be preserved in one specimen from collection AFT-X 400 (Fig. 5.6, 5.7), but it is difficult to determine whether these are truly filae or features caused by exfoliation of the shell surface. Their regular spacing along the flanks of ribs suggests that these may, in fact, be part of the shell structure. Altaethyrella tarimensis n. sp. is very similar to A. otarica
from the Chu-Ili range in Kazakhstan (Nikitin et al., 2006); both are nearly identical in profile and outline, although A. tarimensis n. sp. is slightly more convex and wider (but similar to a collection from the Odak Beds of Kazakhstan), and shells usually have fewer ribs (although shells from the Koskarasu
Figure 4. Association between Altaethyrella tarimensis n. sp. encrusted by both ramose (left) and treptostome bryozoans. The bryozoans cross the commissure of both brachiopod shells, indicative of post-mortem encrustation. (1–4) NIGP 167279 from collection AFT-X 398, anterior, magnified anterior, ventral, and lateral views of conjoined shell with calcite vein; (5–7) NIGP 167280 from collection AFT-X 400, anterior, dorsal, and lateral views of conjoined shell. Scale bars are (1, 3–7) 5mm and (2) 2mm.
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