62 



L.E. POPOV, L.R.M. COCKS AND I.F. NIKITIN 



Genus PHACELOORTHIS Percival, 1991 



Type species. P. decoris Percival, 1991, from the Quondong 

 Limestone (Caradoc) of New South Wales, Australia. 



Phaceloorthis? sp. 



PI. 11, figs 13, 14 



Material. One pair of conjoined valves (BC 57531) (L=20.8, 

 W=25.6, T=9.8) from Sample 2538, Kujandysai, near Akchoku 

 Mountain. 



Description. Shell subequally biconvex, transversely subrect- 

 angular in outline with hinge line somewhat shorter than maximum 

 shell width at mid-length. Anterior margin rectimarginate. Ventral 

 valve moderately convex in lateral profile with maximum thickness 

 at one-third valve length. Ventral interarea almost orthocline, slightly 

 curved in cross-section with open, narrow triangular delthyrium. 

 Dorsal valve moderately convex with maximum thickness near the 

 mid-valve. Umbonal area with shallow sulcus fading towards mid- 

 valve. Dorsal interarea anacline, planar, linear. Shell surface with 9 

 low, angular radial plications and sumperimposed finely fascico- 

 stellate ribs 7-9 per 3 mm along the anterior margin. Interior of both 

 valves unknown. 



Discussion. The interior of this species remains unknown, which 

 makes its generic attribution highly provisional, but there are only a 

 few impunctate mid and late Ordovician orthide genera with 

 fascicostellate ornament and they are mostly related to the family 

 Giraldiellidae. Otherwise fascicostellate ribbing is characteristic of 

 the plectorthid genus Phaceloorthis. This single specimen somewhat 

 resembles Phaceloorthis recondita Popov, Nikitin & Cocks, 2000 

 from the Otar Member (Upper Caradoc ) of the Dulankara Moutains in 

 its general shell shape and size and fascicostellate ornament, but differs 

 in having an orthocline ventral interarea and weak radial plications. 



Family WANGYUHDAE Zeng, 1989 

 Genus BOWANORTHIS Percival, 1991 



Type species. Bowanorthis fragilis Percival, 1991, 

 Caradoc of New South Wales, Australia. 



from the 



Bowanorthis! devexa sp. nov. PI. 11, figs 23-37; Fig. 14 



Etymology . After devexus, Latin - hollow. 



Holotype. BC 57532, PL 1 1 , figs 23-27, conjoined valves, from 

 the Anderken Formation, Sample 2538, Kujandysai, near Akchoku 

 Mountain. 



Material. Twelve conjoined valves from Samples 2538 (BC 

 57178, 57532-34), 8217 (BC 57179) Kujandysai, near Akchoku 

 Mountain; Sample 948 (BC 57172-77), Tesik River. 



Description. Shell ventribiconvex, slightly transverse and 

 semioval, about 85-98% as long as wide with hinge line slightly 

 shorter than maximum width at one-quarter shell length. Anterior 

 commissure sulcate. Ventral valve carinate posteriorly, strongly 

 convex in lateral profile with maximum thickness at about one-third 

 valve length. Beak small, erect. Ventral interarea apsacline, incurved 

 in cross-section, with small subtriangular delthyrium. Ventral me- 

 dian fold originating at the umbonal area with steep lateral slopes 

 flanked by folds. Lateral sides of the valves less convex. Dorsal valve 

 evenly convex with linear, anacline interarea and deep, V-shaped 

 median sulcus originating at the beak and ending in a low semioval 

 tongue occupying slightly less than half of the valve length. Radial 

 ornament fascicostellate with three strong angular ribs and 4-5 

 costellae per mm along the anterior margin of mature specimens. 

 Interior of both valves unknown. 



Measurements. Conjoined valves; (58/12375) L=6.4, W=6.7, 

 T=3.8. Sw=3.3; (59/12375), L=4.5, W=4.6, T=2.7, Sw=2.6; (60/ 

 12375), L=4.8,W=5.6,T=3.1,Sw=2.4. 



Discussion. This species is provisionally included within 

 Bowanorthis because of the small ventribiconvex shell with strongly 

 sulcate anterior commissure, carinate ventral valve, fascicostellate 

 ornament and receding dental plates, all resembling B. fragilis from 

 the Caradoc of New South Wales (Percival 1991 ); however, it differs 

 in having a strongly apsacline ventral interarea and a less transverse 

 shell outline. The general morphology of the cardinal process and 

 brachiophores in the Kazakh species looks similar to B. fragilis, but 

 the presence of the characteristic sigmoidal plates is impossible to 



Fig. 14 Transverse serial sections of Bowanorthis! devexa sp.nov. from Sample 2538. Kujandysai section. Distance in mm is measured from the posterior 

 tip of ventral beak. Dorsal valve uppermost. Also reconstructions of the ventral and dorsal interiors. 



