76 



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



from Samples 100 (=K-98/1970) (BC 56656-9), 626, 843 (BC 

 5758 1-83), Anderkenyn-Akchoku section; Samples 628 (BC 5666 1 ), 

 2538 (BC 57580), 7613 (BC 56649-55), Kujandysai Section; Sam- 

 ple 948 (BC 5731 1-2), Tesik River. 



Description. Shell dorsibiconvex to biconvex, slightly transverse, 

 about 73% as thick as long and about 75% as long as wide with 

 maximum width at mid-length. Anterior commissure uniplicate. 

 Ventral valve moderately convex in lateral profile with maximum 

 thickness at quarter valve length from the slightly curved, pointed 

 beak. Delthyrium open, narrow triangular. Ventral sulcus originating 

 2-3 mm from the umbo, very shallow posterior to mid-valve, but 

 deepening anteriorly and terminating in low, trapezoidal tongue 

 about 79% valve width. Dorsal valve moderately and evenly convex 

 in lateral profile with shallow umbonal sulcus inverting into a low 

 flattened median fold with steep lateral slopes. Radial ornament of 

 coarse angular ribs, usually with 4 ribs in the dorsal median fold, 3 

 ribs in the sulcus and 6-8 on flanks of both valves. 



Ventral interior with cyrtomatodont teeth and short, thin dental 

 plates flaring close to the sides of the valve. A pedicle base impres- 

 sion occupies the floor of the delthyrial cavity; large, weakly 

 impressed ventral muscle field with small, lanceolate adductor scars 

 completely surrounded by diductor scars anteriorly. Dorsal interior 

 with disjunct hinge plate and narrow cruralium bearing a simple, 

 ridge-like cardinal process and long, high median ridge extending 

 anteriorly to mid-valve. Adjuster scars weakly impressed with pos- 

 terior and anterior pair of about equal size, separated by fine, oblique 

 transmuscle ridges. 



Measurements. (471/1 2375) conjoined valves, L=14.0,W=16.9, 

 T=6.3, Sw=8.9; (474/12375) conjoined valves, L=20.4, W=21.0, 

 T=11.2, Sw=8.7; (475/12375) conjoined valves, L=22.9, W=24.5, 

 T=10.2, Sw=12.8; (476/12375) conjoined valves, L=16.5, W=19.8, 

 T=6.5, Sw=11.2; (479/12375) conjoined valves, L=10.5, T=6.7, 

 Sw=6.7. 



Discussion. Rhynchonellides are widespread in the mid and late 

 Ordovician shallow-water benthic assemblages of Kazakhstan, but 

 with few exceptions are represented exclusively by ancystrorhynchids 

 and oligorhynchids (Nikiforova & Popov 1981; Nikitin & Popov in 

 Klenina et al. 1 984). All other Kazakh rhynchonellide species previ- 

 ously described as Rhynchotrema by Rukavishnikova (1956) and 

 Klenina (in Klenina et o/. 1 984) belong in reality to the 

 ancystrorhynchid Altaethyrella or atrypides related to Nalivkinia 

 (Popov et al. 2000). This species represents the earliest known 

 record of rhynchonellides with the cruralium supported by the dorsal 

 median septum in Kazakstan. Externally it is similar to Rostricellula 

 sarysuica Nikitin & Popov (Nikitin et al. 1996) from the Upper 

 Caradoc to Lower Ashgill Dulankara Regional Stage of the northern 

 Betpak-Dala Desert, Kazakhstan, but differs in the less convex 

 lateral profile of the dorsal valve, with maximum height at mid- 

 length, the relatively shallow ventral sulcus, and in the presence of a 

 ridge-like cardinal process. 



Rhynchotrema akchokense is similar in radial ornament to two 

 Australian species of the genus, R. oepiki Percival, 1991, from the 



Upper Caradoc of New South Wales, and R. bailliei Laurie, 1991, 

 from the Caradoc of Tasmania, in having a more transverse shell 

 outline, a less convex dorsal valve profile, with maximum height 

 near the mid-length, a relatively shallow ventral sulcus and a low 

 dorsal median fold. R. bailliei is also characterized by its poorly 

 developed cardinal process, which makes its generic assignment 

 somewhat questionable, although we refer it to Rhynchotrema. 



Order ATRYPIDA Rzhonsnitskaya, 1960 



Superfamily LISSATRYPOIDEA Twenhofel, 1914 



Family PROTOZYGIDAE Copper, 1986 



Genus PECTENOSPIRA Popov, Nikitin & Sokiran, 1999 



TYPE SPECIES. Pectenospira pectenata Popov, Nikitin & Sokiran, 

 1999, from the Anderken Formation, Chu-Ili Range. 



Pectenospira pectenata Popov, Nikitin & Sokiran, 1999 



PI. 14, figs 43^6 



1999 Pectenospira pectenata Popov, Nikitin & Sokiran: 648, pi. 

 4, figs 21-32, text-fig. 10. 



Holotype. CNIGR 23/12986, conjoined valves, from the 

 Anderken Formation, Sample 2538, Kujandysai section. 



Material. 23 conjoined valves, two ventral and one dorsal valve, 

 from Samples 100 (=K-98/1970), 626 Anderkenyn-Akchoku sec- 

 tion; Samples 628, 2538 (BC57363), 8257, Kujandysai Section; 

 Sample 948 (BC 57314-20), Tesik River. 



Discussion. This species was described and discussed in detail by 

 Popov etal. (1999). 



Order ATHYRIDIDA Boucot, Johnson & Staton, 1964 



Suborder ATHYRIDIDINA Boucot. Johnson & Staton. 1964 



Superfamily MERISTELLOIDEA Waagen, 1883 



Family MERISTELLIDAE Waagen, 1883 



Genus KELLERELLA Nikitin & Popov in Nikitin, Popov & 



Holmer, 1996 



TYPE SPECIES. Kellerella ditissima Nikitin & Popov in Nikitin et 

 al. (1996), from the Dulankara Regional Stage (Upper Caradoc), 

 north Betpak-Dala, Kazakhstan. 



Kellerella misiusi Popov, Nikitin & Sokiran, 1999 



PL 14, figs 58-61 



Holotype. CNIGR 26/1 2986, conjoined valves from the Anderken 

 Formation, Sample 2538, Kujandysai section. 



Material. 72 pairs of conjoined valves and one dorsal valve, from 

 Samples 100 (=K-98/1970), 626, Anderkenyn-Akchoku section; 

 Sample 8214 (BC56773, 57334-9), west side of Aschisu River; 

 Samples 628. 2538, Kujandysai Section. 



Table 29 Measurements of ventral valves of Nikolaispira guttula sp. nov.. Sample 948, Tesik river. 





L 



W 



T 



Ld 



Sw 



St 



LAV 



T/L 



Sw/W 



N 



13 



13 



13 



13 



13 



13 



13 



13 



13 



X 



6.5 



5.6 



4.2 



6.0 



2.9 



1.2 



117% 



64% 



52% 



s 



0.72 



0.57 



0.66 



0.70 



0.45 



0.29 



5.2 



5.1 



5.8 



MIN 



5.6 



4.9 



2.8 



5.0 



2.2 



0.5 



110% 



50% 



42% 



MAX 



7.6 



6.7 



5.3 



7.2 



3.6 



1.6 



127% 



70% 



62% 



