UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



61 



fifths as long as the valve. Mantle canal system saccate with short, 

 diverging vascula media. Dorsal interior with blade-like cardinal 

 process situated on a high subtriangular notothyrial platform. 

 Brachiophores high, subtriangular with strongly thickened, slightly 

 divergent bases. Adductor field weakly impressed, quadripartite, 

 bisected by a low median ridge. Anterior adductors larger than 

 posterior ones. 



Measurements. Conjoined valves; [BC 56507, L=22.2, W=24.0. 

 T=12.2, Sw=14.4, St=6.4; BC 56508, L=25.1, W=26.3, T=14.8. 

 Sw=14.6, St=6.8]. 



DISCUSSION. This species can be distinguished from other species 

 of the genus such as Austinella whitfieldi (Winchell & Schuchert) 

 and A. kankakensis (McChesney), re-described by Wang (1949) 

 from the Ashgill Maquoketa Formation of Iowa, by its uniplicate 

 anterior commissure with the dorsal sulcus reversed into the median 

 fold posterior to the mid-valve. 



Superfamily PLECTORTHOIDEA Schuchert, 1929 



Family PLECTORTHIDAE Schuchert, 1929 



Subfamily PLECTORTHINAE Schuchert, 1929 



Genus PLECTORTHIS Hall & Clarke, 1892 



TYPE SPECIES. Orthis plicatella Hall, from the Cincinnatian (Lower 

 Ashgill), of the U.S.A. 



Plectorthisl burultasica sp. nov. PL 10, fig. 43, PL 11, figs 

 3-12 



1985 Plectorthis afi. a/to'ra Severgina; Popov: 51, pi. 1, figs 1,2. 



ETYMOLOGY. After the type locality in the Burultas Valley. 



HOLOTYPE. BC 57528, PL 11, figs 3^1, dorsal valve, Anderken 

 Formation, Sample 7613, Akchoku Mountain, Kujundysai section. 



Material. Five conjoined valves, 8 ventral and 9 dorsal valves 

 from Samples 2538, 7613 (BC 57528), Kujandysai near Akchoku 

 Mountain; Sample 626 (BC 57170, 71), 843, 8128 (BC 57530), 

 Anderkenyn-Akchoku; all Chu-Ui Range; Sample 1041a (BC 57529), 

 Burultas Valley; Sample 1018 (BC 57367), 7 km southwest of 

 Karpkuduk well, Kotnak mountains, south Betpak-Dala. 



DESCRIPTION. Shell subequally biconvex, transversely subrect- 

 angular in outline, about 60% as thick as long and three-quarters as 



long as wide, with maximum width at mid-length. Cardinal extremi- 

 ties obtuse to slightly rounded. Anterior commissure rectimarginate. 

 Ventral valve moderately and gently convex in lateral profile with 

 low, strongly apsacline interarea slightly curved in cross-section. 

 Dorsal valve moderately and evenly convex in lateral profile with 

 low, linear, orthocline interarea and shallow umbonal sulcus fading 

 at mid-length. Radial ornament of 28-32 rounded costellae bifurcat- 

 ing at the posterior half of the shell and separated by interspaces of 

 about equal width as ribs. Radial rows of fine rounded exopunctae on 

 both sides of each rib. 



Ventral valve with teeth supported by thin diverging dental plates 

 about one-third shorter than length of the elongate subpentagonal 

 muscle field. Adductor scar narrow triangular, slightly raised 

 anteriorly, about the same length as strongly impressed diductor 

 scars. Dorsal valve interior with high, triangular brachiophores with 

 bases converging anteriorly. Notothyrial platform high and narrow, 

 crossed by ridge-like cardinal process with crenulated myophore. 

 Median ridge strong, extending anteriorly to mid-valve. Dorsal 

 anterior and posterior adductor scars about equal size, separated by 

 fine, slightly oblique, transverse ridges. 



Discussion. Criteria for generic separation amongst the 

 Plectorthidae require revision. The type species of Plectorthis, P. 

 plicatella, has never been fully revised, although Schuchert & Cooper 

 (1932, pi. 11, figs 4, 9) illustrated ventral and dorsal interiors from 

 the Maysville Formation of Cincinnati, Ohio. Material labelled as P. 

 plicatella in the Natural History Museum (eg. BB 14835) from 

 Cincinnati includes well preserved exteriors with no trace of 

 exopunctae. However, our new species has well-developed rows of 

 exopunctae on both sides of each costa, as have other species 

 attributed to Plectorthis, e.g. Plectorthisl punctata illustrated by 

 Cooper (1956), P. obesa, mentioned but not illustrated by Cooper 

 (1956), and the Plectorthis sp. of Neuman (1971:21). Thus, until 

 comparable exopunctae have been found in true P. plicatella, we 

 attribute the exopunctate species to Plectorthis with a query. 



Plectorthisl burultasica resembles Plectorthis altaica Severgina, 

 1967 from the Khankhara Formation (Caradoc) of Gornyi Altai in 

 radial ornament, size and outline, but differs in having a weak 

 umbonal dorsal sulcus fading to the mid-valve and a more 

 ventribiconvex profile. Plectorthisl punctata has a slightly sulcate 

 dorsal valve by comparison with PI burultasica as well as fewer rib 

 bifurcations. It is also considerably smaller. In addition, P.l obesa 

 has a more strongly convex dorsal valve and fewer bifurcations in the 

 ribbing. 



PLATE 11 



Figs 1, 2 Dolerorthis expressa Popov, Sample 8137, Anderkenyn-Akchoku section. BC 57526, dorsal internal mould, x 2. and latex of external mould, x 

 6. 



Figs 3-12 Plectorthis? burultasica sp. nov. 3, 4. Sample 7613, Akchoku Mountain. Kujandysai section. BC 57528. holotype. dorsal latex cast and internal 

 mould, x 2. 5-8, Sample 1041a, Burultas, BC 57529, conjoined valves, lateral, posterior, ventral and dorsal views, x 2. 9-11. Sample 1018, area 7 km 

 SW of Kotnak mountains, south Betpak-Dala, CNIGR 1/1 1989, conjoined valves, dorsal, ventral and lateral views, x 2. 12, Sample 8128. Anderkenyn- 

 Akchoku section, BC 57530. ventral exterior, latex cast, x 2. 



Figs 13, 14 Phaceloorthisl sp. Sample 2538, Akchoku Mountain, Kujandysai section, BC 57531, conjoined valves, ventral and dorsal views, x 1 .5. 



Figs 15-22 Austinella sarybulakensis sp. nov. Sample 85258, east side of Kujandysai. 15-18, BC 56507, conjoined valves, holotype, ventral, lateral, 

 anterior and dorsal views, x 1.5. 19, BC 56508. conjoined valves, posterior view, x 1.5. 20. BC 56505, ventral interior, x 2. 21, 22, BC 56506, dorsal 

 internal mould and latex cast, x 2. 



Fig. 23-37 Bowanorthisl devexa sp. nov. Sample 2538, Akchoku Mountain, Kujandysai section. 23-27, BC 57532, conjoined valves, holotype. ventral, 

 lateral, anterior, dorsal and posterior views, x 3. 28-32, BC 57533, conjoined valves, lateral, dorsal anterior, posterior, and ventral views, x 3. 33-37, BC 

 57534, conjoined valves, lateral, posterior, ventral, dorsal and anterior views, x 3. 



Figs 38-44 Phragmorthis conciliata Popov. 38. Sample 1018, area 7 km SW of Kotnak mountains, south Betpak-Dala. CNIGR 1 1/1 1989, ventral internal 

 mould, x 4. 39, Sample 76 1 3, Akchoku Mountain. Kujandysai section. BC 57535, ventral internal mould, x 5. 40^12, Sample 2538, Akchoku Mountain, 

 Kujandysai section, BC 57536, conjoined valves, lateral, dorsal and ventral views, x 4. 43, 44. Sample 626. Anderkenyn-Akchoku section. BC 57537. 

 ventral exterior and lateral view, x 4. 



