UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



53 



ORTHOTETIDA Waagen, 1884 



Suborder ORTHOTETIDINA Waagen, 1884 



Superfamily CHILIDIOPSOIDEA Boucot, 1959 



Family CHILIDIOPSIDAE Boucot. 1959 



Subfamily GACELLINAE Williams & Brunton, 2000 



Genus GACELLA Williams, 1962 



TYPE SPECIES. Gacella insolita Williams, 1962, from the Stinchar 

 Limestone (Lower Caradoc), Girvan, Scotland. 



Gacella institata sp. nov. PI. 8, figs 21-33, PI. 9, figs 1-4 



Etymology. After instita, Latin - a swathe. 



HOLOTYPE. BC 57500, PI. 8, figs 32, 33, from the Anderken 

 Formation, Sample 100, Anderkenyn-Akchoku section. 



Material. 10 pairs of conjoined valves, 2 ventral and 8 dorsal 

 valves, from Samples 100 (=K-98/1970) (BC 57496, 98. 99, 57500), 

 626 (BC 57497), Anderkenyn-Akchoku section; Samples 628, 85258 

 (BC 57092-3, 56576), Kujandysai Section.. 



DESCRIPTION. Shell subequally biconvex, transverse, semielliptical 

 in outline about 80% as long as wide, with maximum width at hinge 

 line. Cardinal extremities acute to rectangular. Anterior commissure 

 gently uniplicate. Ventral valve convex in lateral profile with maximum 

 thickness slightly anteriorto the umbo and with flattened sides. Sulcus 

 shallow, originating about 2-3 mm from the umbo. Ventral interarea 

 planar, apsacline with a broad, convex pseudodeltidium perforated 

 apically by a minute foramen. Lateral profile of the dorsal valve gently 

 convex with maximum thickness near the anterior margin. Dorsal 

 median fold low, rounded in cross-section, originating in the umbonal 

 area but very weakly defined until the mid-valve. Dorsal interarea 

 planar, anacline, with convex chilidium. Radial ornament unequally 

 parvicostellate with two to three generations of acentuated ribs, about 

 4-5 per 3 mm along the anterior margin of mature specimens. 

 Concentric ornament of numerous fine growth lamellae anteriorly. 



Ventral interior with teeth supported by long subparallel but 

 slightly divergent dental plates and narrow, elongate subtriangular 

 muscle field divided by median ridge. Numerous fine crenulations 

 on the outer surface of the teeth. Dorsal interior with bilobed cardinal 

 process on a high notothyrial platform: adductor scars elongated 

 slightly, shorter than half valve length, crossed by two pairs of short 

 transmuscle septa. Median ridge fine and faint, originating some 

 distance from the notothyrial platform. 



Measurements. (47 1/12375) conjoined valves, L=l 4.0, W= 1 6.9, 

 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. This species differs from others of the genus in 

 having a concentric ornament of strong growth lamellae and coarser 

 accentuated ribs. It can be compared to Gacella ponderosa Williams, 

 1962, from the Confinis Formation (Llandeilo) of Girvan, south 

 Scotland, in the general shape and size of the shell, but differs in 

 having a less convex lateral profile in both valves in addition to the 

 patterns of radial and concentric ornament. 



Gacella institata differs from G. sulcata Misius (in Misius & 

 Ushatinskaya 1 977), from the Tabylgaty Formation (Upper Caradoc) 

 of the Moldo-Too Range, Kyrgizstan. in having a shallow ventral 

 median sulcus and low dorsal median fold usually originating in the 

 umbonal region; the convex, not flat, lateral profile of the ventral 

 valve, and in the absence of geniculation in the dorsal valve. 



Suborder TRIPLESHDINA Moore, 1952 



Superfamily TRIPLESIOIDEA Schuchert, 1913 



Family TRIPLESIIDAE Schuchert, 1913 



Genus TRIPLESIA Hall, 1859 



Type SPECIES. Atrypa e.xtans Emmons, from the Trenton Group 

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



Triplesia sp. 



PI. 9, figs 22-26 



Material. Two ventral and three dorsal valves (BC 575 12) from 

 Sample 8228. Kopalysai. 



DESCRIPTION. Shell dorsibiconvex, transverse suboval in outline, 

 about 80% as long as wide with uniplicate anterior commissure. 

 Ventral valve moderately convex, with maximum thickness at about 

 one-third valve length. Ventral interarea anacline. Sulcus originating 

 near mid-valve, strongly deepening anteriorly, flanked laterally by 

 angular plications. Dorsal valve moderately convex with swollen 

 umbo. Strong median fold with steep sides, originating anteriorly of 

 mid-valve, bisected medianly by fine groove. Shell surface smooth 

 with rare, slightly irregular growth lamellae anteriorly. Ventral inte- 

 rior with teeth supported by short subparallel dental plates. Dorsal 

 interior with forked cardinal process on a short shaft. 



Measurements. 

 T=4.5. 



(488/12375) dorsal valve, L=16.2, W=16.9, 



Discussion. These shells are comparable with large specimens of 

 Triplesia aff. subcarinata, but differ in having a narrow groove 

 bisecting the dorsal median fold and a ventral sulcus which is more 

 rounded in cross-section and a dorsal median fold. However, the 

 shape of the dorsal fold and ventral sulcus varies significantly and it 

 is difficult to evaluate observed morphological differences in this 

 species because of the small number of shells available. 



Triplesia aff. subcarinata Cooper, 1956 



PI. 10, figs 1-8, 19 



Material. 6 conjoined valves, 2 ventral and 3 dorsal valves from 

 Samples 100 (=K-98/1970), 626 (BC 57515), 8251a (BC 57514), 

 Anderkenyn-Akchoku section; Samples 85258 (BC 57094-5), 

 Kujandysai section; Sample 1041a, Burultas Valley. 



Discussion. This species resembles Triplesia carinata Cooper, 

 1956, from the Pratt Ferry Formation of Alabama and T subcarinata 

 Cooper, 1956, from the Lebanon Formation of Tennessee, as well as 

 specimens of that species from the Bestamak Formation (Llandeilo- 

 Lower Caradoc) of the Chingiz range. Kazakhstan (Nikitin & Popov 

 in Klenina et at. 1984), in having a well-developed sulcus and a 

 carinate dorsal median fold originating near the mid length, but it 

 differs from both in having a larger shell, a strongly convex lateral 

 profile in the dorsal valve with maximum height near the anterior 

 margin, and a variable transverse profile of the dorsal median fold 

 which has a tendency to be rounded in most specimens. Triplesia aff. 

 subcarinata differs from T ainca Severgina, 1978, from the Lower 

 Ashgill Gurianovka Formation and Marinikha Limestone of the 

 Sayano-Altai Mountain Region in having a strongly dorsibiconvex 

 lateral profile with a slightly accentuated ventral beak erect 

 posteriorly, a narrow ventral sulcus and a dorsal median fold usually 

 rounded in cross-section. 



Genus BICUSPINA Havh'cek, 1950 



TYPE SPECIES. Orthis cava Barrande, 1848, from the Lower 

 Caradoc of Bohemia. 



