30 



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



Description. Shell planoconvex, subcircular, ornamented by 

 strong rounded irregular concentric rugellae of 10-11 per 3 mm. 

 Ventral valve low, subconical with maximum height at the umbo 

 which is situated about 10% of the valve length from the posterior 

 margin. Pedicle foramen small, rounded, located at the end of narrow 

 pedicle track covered by listrium. Dorsal valve flat with submarginal 

 umbo. Interior of both valves not observed. 



Nushbiella dubia (Popov, 1977) 



PL 1 , figs 13, 14 



Measurements. 

 T=4.8. 



BC 57590, conjoined valves, L=14.8, W=14.4, 



Discussion. These specimens resemble Schizotreta triangularis 

 Popov (Nikitin et al. 1996: 85) from the late Caradoc Dulankara 

 Regional Stage of the northern Betpak-Dala Desert, Central 

 Kazakhstan, but differ in their subcircular valve outline, ventral 

 umbo situated close to the posterior margin and strong, irregular 

 concentric rugellae. In concentric ornament they somewhat resemble 

 Schizotreta corrugata Cooper ( 1956: 277) from the Llandeilo Pratt 

 Ferry Formation of Alabama, USA, but can be distinguished in 

 having a larger size, more circular shell outline and more densely 

 spaced concentric rugellae. 



Order SIPHONOTRETIDA Kuhn, 1949 



Superfamily SIPHONOTRETOIDEA Kutorga, 1848 



Family SIPHONOTRETIDAE Kutorga, 1848 



Genus MESOTRETA Kutorga, 1848 



Type species. Siphonotreta tentorium Kutorga, 1848: 270, from 

 the Arenig (Volkhov Regional Stage), north-western Russia. 



DISCUSSION. The type material of Mesotreta tentorium is lost and 

 its taxonomic position within the Siphonotretoidea is unclear. At 

 present, our knowledge of the type species of this genus is based on 

 a single incomplete ventral valve from the Upper Volkhov Stage 

 (Holmer & Popov 2000: Fig. 79,2). Mesotreta is unique among the 

 Siphonotretida because of its low conical ventral valve with small, 

 slightly eccentric pedicle foramen, but it possesses the hollow spines 

 characteristic of this order. The ventral interior and dorsal valve of 

 Mesotreta remain unknown. 



Mesotreta? sp. 



PI. l,figs 11, 12 



1 986 Nushbiella dubia (Popov); Kolobova & Popov: pi. 1 , fig. 1, 

 non fig. 2. 



Material. One ventral valve (CNIGR 1/12361) from Sample 

 100, Anderkenyn-Akchoku section. 



DESCRIPTION. Valve slightly transverse, elliptical in outline; low, 

 subconical with eccentric umbo at 20% of valve length from the 

 posterior margin. Foramen small, slightly elongate, suboval. Con- 

 centric ornament of up to 16 thin, evenly spaced, crowded growth 

 lamellae and numerous fine hollow spines. Ventral interior and 

 dorsal valve unknown. 



DISCUSSION. This unnamed species resembles Siphonotreta tento- 

 rium in having a low conical ventral valve lacking a well-defined 

 pseudointerarea and small umbonal pedicle foramen, but the 

 Kazakhstanian specimen differs in its strongly developed lamellose 

 ornament and more posterior ventral umbo. 



Genus NUSHBIELLA Popov in Kolobova & Popov, 1986 



TYPE SPECIES. Multispinula? dubia Popov, 1977; from the 

 Bestamak Formation, Tselinograd Regional Stage (Llandeilo), 

 Chingiz Range, Kazakhstan. 



1977 Multispinula? dubia Popov: 104, pi. 25, figs 8-11. 



1986 Nushbiella dubia (Popov) Kolobova & Popov: 251, pi. 1, 



fig. 2, non fig. 1 . 

 2000 Nushbiella dubia (Popov) Holmer & Popov: fig. 79, 6a, b. 



Holotype. CNIGR 1/10847, ventral valve, Bestamak Formation 

 (Llandeilo), locality 553a, east side of Chagan River near Konur- 

 Aulie cave. Chingiz Range, Kazakhstan. 



Material. One ventral and one dorsal valve from Sample 8223a, 

 Anderkenyn-Akchoku section; Sample 2538 (BC 57591), Kujandysai 

 section. 



Discussion. The specimens from the Anderken Formation have 

 no significant differences from the rather older topotypes in orna- 

 ment and external shell morphology. 



Order CRANIOPSIDA Gorjansky & Popov, 1985 



Superfamily CRANIOPSOIDEA Williams, 1963 



Genus PARACRANIOPS Williams, 1963 



TYPE SPECIES. Craniops pararia Williams, 1962, from the Lower 

 Ardmillan Series (Caradoc), Girvan, Scotland. 



Paracraniops sp. 



PI. 1, fig. 15 



Material. One dorsal internal mould, BC 57377, from Sample 

 8128a, Anderkenyn-Akchoku section. 



Discussion. A single specimen represents the earliest record of 

 craniopsides from Kazakhstan. There is little doubt of the generic 

 attribution, but there is insufficient material to allow detailed com- 

 parison with other named species of the genus. 



Order STROPHOMENIDA Opik, 1934 



Superfamily STROPHOMENOIDEA King, 1846 



Family STROPHOMENIDAE King, 1846 



Subfamily STROPHOMENINAE King, 1846 



Genus LONGVILLIA Bancroft, 1933 



Type SPECIES. Orthis grandis J.de C. Sowerby, 1839, from the 

 Cheney Longville Flags (Lower Caradoc), Shropshire, England. 



Longvillia lanx (Popov, 1985) 



PI. 1, figs 16-21 



1985 Strophomena /<mv Popov: 58; pi. 1, fig. 13; pi. 2, figs 12, 13; 



pi. 3, fig. 1. 

 1 985 Strophomena digna Popov: 67 nomen erratum, pi. 1 , fig. 13. 



Holotype. CNIGR 30/11989, ventral internal mould, from the 

 Anderken Formation, Sample 1 1 8a, 7 km south-west of Karpkuduk 

 well, Kotnak Mountains, refigured here (PI. 1, fig. 21). 



Material. Two pairs of conjoined valves, 1 1 ventral and 8 dorsal 

 valves from Samples 1018, 1018a, 7 km south-west of Karpkuduk 

 well, Kotnak Mountains. 



Description. Shell very gently convexiconcave, slightly trans- 

 verse, subrectangular in outline with maximum width about 

 one-quarter of the valve length from the hinge line. Anterior com- 

 missure rectimarginate. Ventral valve gently and evenly concave in 

 profile with a slightly raised, pointed umbo and steeply apsacline 

 ventral interarea bearing large, convex pseudodeltidium. Dorsal 

 valve evenly convex with flattened umbonal area. Radial ornament 



