UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



Table 20 Measurements of complete shells of Dolerorthis pristina sp. 

 nov.. Samples 100 and 626 from Anderkenyn-Akchoku section. 





Lv 



W 



T 



Iw 



Lv/W 



T/L 



IwAV 



N 



10 



10 



6 



10 



10 



6 



9 



X 



10.0 



11.8 



4.2 



10.3 



85.2% 



47.6% 



87.9% 



s 



3.04 



3.36 



1.11 



2.63 



10.0 



6.5 



9.5 



MIN 



5.9 



7.5 



2.8 



6.5 



70.2% 



40.0% 



75.0% 



MAX 



14.2 



18.2 



5.5 



13.7 



103.6% 



56.3% 



100.0% 



Description. Shell weakly ventribiconvex, slightly transverse, 

 suboval in outline, on average 82% (S=7.0, N=10) as long as wide 

 and 48% (S=6.0, N=6) as high as long. Anterior commissure slightly 

 shorter than maximum shell width at mid-length. Cardinal extremi- 

 ties obtuse. Anterior commissure rectimarginate or weakly sulcate. 

 Radial ornament costellate with up to 1 7 primary costae and costellae 

 branching near the mid-length and near the anterior and lateral 

 margins. 6-8 costellae per 3 mm along the anterior margin and 

 varying from 31 to 54 in full-grown specimens. 



Ventral valve moderately and unevenly convex with maximum 

 thickness at about one-third valve length from the small, pointed 

 beak. Ventral interarea apsacline, slightly curved in cross-section 

 with open, narrow delthyrium. Dorsal valve weakly convex with 

 maximum thickness slightly anterior from the beak. Interarea low, 

 planar, linear. Shallow sulcus usually well defined in the posterior 

 half of the dorsal valve, but fading anteriorly. 



Ventral interior with small teeth and low, divergent dental plates. 

 Muscle field small, slightly elongate, subpentagonal in outline. 

 Adductor scars narrow, completely separating diductor scars of 

 about equal length. Mantle canals saccate with slightly divergent 

 proximal parts of vascula media. Dorsal valve interior with high, 

 subtriangular brachiophores diverging anteriorly. Cardinal process 

 ridge-like with crenulated myophore. situated on a low subtriangular 

 notothyrial platform. Adductor muscle field subrectangular with 

 anterior adductor scars slightly larger than posterior. Median ridge 

 low and broad, bisecting the entire adductor muscle field. 



DISCUSSION. Dolerorthis pristina differs from D. expressa (Popov 

 1980) in its less convex dorsal valve, much smaller size (less than 

 half D. expressa), and in its evenly convex ventral profile, in contrast 

 to D. expressa in which the ventral profile is relatively flat near the 

 umbo, but increases greatly anteriorly. In addition, D. pristina has 

 finer radial ornament. 



Zeng (1987) erected Paradolerorthis as a subgenus within 

 Dolerorthis. However, his quoted distinctions and equivocal illustra- 

 tions do not allow us to recognize his subgenus as useful, but the type 

 species D. (Paradolerorthis) calla appears similar to D. pristina. 



Family GLYPTORTHIDAE Schuchert & Cooper, 

 Genus GLYPTORTHIS Foerste, 1914 



1931 



Type species. Orthis insculpta Hall, 1 847, from the Richmondian 

 (Ashgill), New York, U.S.A. 



Glyptorthis sp. 



PI. 10, figs 37-42 



Material. Five pairs of conjoined valves, 7 ventral and 6 dorsal 

 valves from Samples 620 (BC 57163, 64), 8223a, Anderkenyn- 

 Akchoku; Sample 8214, Ashchisu River; Samples 2538 (BC 

 57 166-69, 57524), 8256, Kujandysai near Akchoku Mountain; Sam- 

 ple 628 (BC 57165, 57525), east side of Kujandysai; Sample 948, 

 Tesik River. 



Description. Shell slightly ventribiconvex, transverse, rounded 



59 



subrectangular in outline, about 80% as long as wide. Hinge line 

 slightly narrower than maximum shell width at mid-length. Cardinal 

 extremities slightly obtuse. Anterior commissure varying from 

 slightly sulcate to rectimarginate. Ventral valve moderately convex 

 with maximum thickness at umbo. Interarea moderately high, trian- 

 gular, planar, catacline, divided by narrow triangular, open delthyrium. 

 Dorsal valve gently convex with maximum thickness at about one- 

 quarter valve length from the beak. Dorsal sulcus shallow and 

 narrow, originating at umbo and fading anteriorly. Dorsal interarea 

 low, linear, orthocline. Radial ornament coarsely costellate with up 

 to 16 primary ribs and 25-30 costellae (up to 5 costellae per 3 mm) 

 in adult specimens. Secondary costellae in the median part of the 

 dorsal valve bifurcate internally. Concentric ornament of crowded, 

 evenly spaced growth lamellae. 



Ventral interior with teeth supported by short and high dental 

 plates. Muscle field small, situated entirely within delthyrial cham- 

 ber. Mantle canals saccate with straight, slightly diverging anteriorly 

 vascula media. Dorsal interior not observed. 



DISCUSSION. These specimens closely resemble Glyptorthis 

 balcletchiensis (Davidson, 1883) from the Upper Caradoc of the 

 Girvan District, Scotland (Williams 1962) in the size, general outline 

 and convexity of the shell, as well as in the number and bifurcation 

 of the costellae. It differs from another coarsely ribbed Kazakh 

 species Glyptorthis? bestamaki Nikitin & Popov (in Klenina et al. 

 1984) from the lower Bestamak Formation (Nemagraptus gracilis 

 Zone) of the Chingiz Range in having a rectimarginate or slightly 

 sulcate anterior commissure and a dorsal sulcus not reversed anteriorly 

 into the median fold. 



Family PLAESIOMYIDAE Schuchert, 1913 

 Genus AUSTINELLA Foerste, 1909 



Type SPECIES. Orthis kankakensis McChesney, from the 

 Maquoketa Formation (Ashgill) of Iowa, U.S.A. 



Austinella sarybulakensis sp. nov. PI. 11, figs 15-22 



Etymology. After Sarybulak River, 10 km west of the type locality. 



HOLOTYPE. BC 56507, PI. 11. figs 15-18, conjoined valves; 

 Anderken Formation, Sample 85258, east side of Uzunbulak River. 



Material. Three conjoined valves, one ventral and one dorsal 

 valve from Sample 85258 (BC 56505-8), east side of Uzunbulak 

 River; Sample 818a, Burultas Valley. 



Description. Shell subequally biconvex, transverse, subrect- 

 angular in outline about 93-97% as long as wide and 54-60% as 

 thick as long. Hinge line somewhat shorter than maximum shell 

 width at the mid-length. Anterior commissure uniplicate. Ornament 

 costellate with 8-9 costellae per 5 mm along the anterior margin and 

 25-28 primary ribs near the umbo. Ventral valve moderately convex 

 with maximum thickness slightly anterior to the umbo. Ventral 

 pseudointerarea high, triangular with open, triangular delthyrium. 

 Shallow sulcus originating at about 7 to 9 mm anterior to the beak, 

 widening and deepening anteriorly. Lateral sides of the valve gently 

 and evenly convex in transverse section. Dorsal valve moderately 

 and unevenly convex. Dorsal interarea low, planar, orthocline. Shal- 

 low dorsal sulcus in the umbonal area reverses into a median fold at 

 5-7 mm from the umbo. 



Ventral interior with strong teeth and short, slightly divergent 

 dental plates. Muscle field strongly raised anteriorly in a form of 

 pseudospondylium, rounded subtriangular in outline, about two- 



