44 



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



Shlyginia fragilis (Rukavishnikova, 1956) PI. 6, figs 1 1-25 



1956 Dulankarella fragilis Rukavishnikova: 136, pi. 2, figs 16- 



23. 

 1996 Shlyginia fragilis (Rukavishnikova) Nikitin & Popov: 7. 



Holotype. IGNA 28/1369, conjoined valves; Anderken Forma- 

 tion, east side of Kopalysai River. 



Material. Eight pairs of conjoined valves, 57 ventral and 53 

 dorsal valves from Samples 100b (BC 56989), 620 (BC 56991-99), 

 843, 8128a, 8128b, 8135, 8137 (BC 57450), Anderkenyn-Akchoku 

 section; Samples 628, 7613, 8258, Kujandysai section; Samples 1 10, 

 8230 (BC 57453), 8257, Buldukbai-Akchoku; Sample 8228 (BC 

 12881-88, 57447, 48, 52), east side of Kopalysai River; Samples 

 390, 818 (BC 57451), 1041a, Burultas Valley; Sample 1018, area 7 

 km south-west from Karpkuduk well, Kotnak Mountains, south 

 Betpak-Dala. 



Description. Shell concavoconvex, transverse, semielliptical in 

 outline, length about two-thirds of the width, with maximum width 

 slightly anterior to hinge line or at the hinge line, and 40% as thick as 

 long. Cardinal extremities acute to slightly rounded. Anterior com- 

 missure rectimarginate. Ventral valve moderately convex in transverse 

 profile with maximum thickness at about one-third of valve length. 

 Interarea low, planar, apsacline with small triangular delthyrium, 

 covered apically by the minute pseudodeltidium. Dorsal valve mod- 

 erately convex, slightly geniculate anteriorly with low, planar, 

 hypercline interarea and notothyrium covered laterally by disjunct 

 chilidial plates. Radial ornament finely parvicostellate with 8-11 

 parvicostellae per mm at the anterior margin and 4-8 parvicostellae 

 between the accentuated costellae which originate in the umbonal 

 area, near the mid-valve and anterior to mid-valve in full grown 

 specimens. 



Ventral valve interior with small teeth lacking dental plates. 

 Muscle field flabellate, on average 80% as long as wide and 40% as 

 long as the valve. Diductor scars large, suboval, deeply impressed 

 and completely enclosing small lanceolate adductor scars bisected 

 by a fine median ridge. Ventral mantle canals saccate with short 

 diverging vascula media. Dorsal interior with a trifid cardinal proc- 

 ess widely diverging, low and short socket ridges and strong median 

 ridge joined anteriorly with the peripheral rim. Dorsal adductor field 

 large, subquadrate. 



Discussion. This species differs from the type species Shlyginia 

 declivis Nikitin & Popov (1983: 238, pi. 3, figs 1-5) in its larger size 

 and moderately concave lateral profile of the dorsal valve, which is 

 also weakly geniculate anteriorly. 



Subfamily PALAEOSTROPHOMENINAE Cocks & Rong, 1989 

 Genus GLYPTAMBONITES Cooper, 1956 



Type species. Glyptambonites musculosus Cooper, 1956, from 

 the Oranda Formation (Caradoc) of Virginia, U.S.A. 



Glyptambonites sp. 



PI. 4, fig. 6 



Material. Three ventral valves, from Sample 628 (BC 56510), 

 Kujandysai, Sample 100, Anderkenyn-Akchoku section. 



DISCUSSION. Glyptambonites is a rare genus in the Anderken 

 Formation and also uncommon in the overlying Dulankara Forma- 

 tion of the Chu-Ili Range. Its internal features are known from 

 specimens from the latter, but not from the Anderken Formation. The 

 exterior of our material appears similar to Glyptambonites glyptus 

 Cooper, 1956 from the Llandeilo to early Caradoc of Virginia and 

 Alabama. 



Genus TESIKELLA gen. nov. 



ETYMOLOGY. After the River Tesik. 



Type SPECIES. Palaeostrophomena necopina Popov, 1980, from 

 the Anderken Formation, Chu-Ili Range. 



Diagnosis. Shell profile resupinate, ventral valve with low interarea; 

 chilidial plates disjunct; radial ornament unequally parvicostellate; 

 ventral interior with double teeth lacking dental plates; ventral muscle 

 field enclosed by bilobed bounding ridges: adductor scars short; 

 ventral subperipheral rim variably developed; dorsal interior with 

 strong median septum coalescing anteriorly with platform. 



DISCUSSION. The subfamily Palaeostrophomeninae has the genera 

 Palaeostrophomena, Apatomorpha, Glyptambonites , Ishimia, 

 Lepidomena, Titanambonites and Toquimia definitely attributed to it, 

 and Goniotrema is possibly a member (Cocks & Rong 2000). Of these, 

 all are of normal convexity apart from Palaeostrophomena which is 

 generally resupinate and Toquimia, in which resupination develops 

 anteriorly in larger specimens. Tesikella is also resupinate and in 

 external features resembles Palaeostrophomena apart from the irregu- 

 larrugae, which are variable in the latter. However, internally Tesikella 

 has a dorsal platform which is absent in Palaeostrophomena, and also 

 has a variably developed subperipheral rim in the ventral valve which 

 in some specimens is fully developed but in others consists only of 

 semi-continuous papillae. The ventral muscle field is enclosed by 

 bilobed bounding ridges, which are not present in other members of 

 the subfamily, but are developed in other Leptellinidae. 



PLATE 6 



Figs 1-6 Tesikella necopina (Popov, 1980), Sample 8129, Anderkenyn-Akchoku section. 1, BC 57433, ventral internal mould, x 2. 2, BC 57434. ventral 

 exterior, x 2. 3, 4, BC 57604, latex cast, x 3, and dorsal internal mould, x 2. 5, 6, BC 57432, latex cast, x 3. and ventral internal mould, x 2. 



Figs 7-10 Sowerbyella (Sowerbyella) rukavishnikovae Popov. 7, Sample 100b, Anderkenyn-Akchoku section. CNIGR 41/1 1522. latex cast of dorsal 

 exterior, x 5. 8, Sample 1 10, Buldukbai-Akchoku section, BC 57801, ventral internal mould, x 4. 9, Sample 1018a, 7 km southwest of Karpkuduk well, 

 Kotnak Mountains, south Betpak-Dala, CNIGR 44/1 1522, dorsal interior, x 2.5. 10, Sample 100b, CNIGR 38/1 1989, dorsal interior, x 2.5. 



Figs 11-25 Shlyginia fragilis (Rukavishnikova). 11, 12, 17-19, 21, 23, 24, Sample 8228, east side of Kopalysai; 11, BC 57448. ventral internal mould, x 

 2; 12, BC 12882, ventral internal mould, x 3; 17-19, BC 57447, ventral, dorsal and lateral views of conjoined valves, x 2; 21, 23, 24, BC 57452, 

 conjoined valves, lateral, dorsal and ventral views, x 2. 13-16. Sample 818, Burultas Valley. BC 57451, conjoined valves, ventral, dorsal and lateral 

 views, x 4; posterior view of interareas, x 6. 20, Sample 8230, BC 57453, dorsal internal mould, x 3. 22, Sample 8137, Anderkenyn-Akchoku section, BC 

 57450, ventral internal mould, x 3. 25, Sample 620, Anderkenyn-Akchoku section, BC 57449, ventral internal mould, x 3. 



Figs 26-33 Sortanella aff. quinquecostata Nikitin & Popov. 26-30, Sample 2538, Akchoku Mountain, Kujandysai section; 26, BC 57488, ventral internal 

 mould, x 2; 27-29, BC56771. conjoined valves, dorsal, ventral and lateral views, x 4; 30. BC 57460, ventral internal mould, x 4. 31, Sample 626, 

 Anderkenyn-Akchoku section, BC 57458. dorsal exterior, x 2. 32, 33, Sample 100, Anderkenyn-Akchoku section, BC 57459, conjoined valves, dorsal 

 and ventral views, x 2. 



