UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



73 



sulcus with a single accentuated primary rib originating in the 

 umbonal area. The coarsely ribbed radial ornament, well defined 

 dorsal median fold and ventral sulcus resembles numerous species of 

 Plectocamara described by Cooper (1956) from the Caradoc of 

 North America, but there is no evidence of the presence of alate 

 plates in the former genus. 



Family PARALELLELASMATIDAE Cooper, 1956 

 Genus SCHIZOSTROPHINA Fu, 1982 



Type species. Schizostrophina margarita Fu, 1 982, from the Jinhe 

 Formation (Caradoc), northwest China. 



DIAGNOSIS (emended). Shell equally biconvex with parasulcate 

 anterior commissure; shallow ventral median sulcus and dorsal 

 median fold originating in umbonal area; radial ornament of variably 

 developed coarse angular ribs in posterior half of the shell; ventral 

 interior with delicate teeth and spondylium supported posteriorly 

 and free anteriorly; dorsal interior with separated outer plates, slightly 

 diverging distally, and well-defined brachial processes. 



Discussion. Schizostrophina was erected originally by Fu ( 1982) 

 without proper illustrations and detailed description of the interior in 

 the type species. However, the very distinctive exterior morphology 



of the shell, which is unique in late Ordovician syntrophiidines, 

 leaves no doubt that the Kazakh shells from the Anderken Formation 

 belong to the same genus and species. Their internal morphology 

 confirms the original assignment of the genus to the Paralellel- 

 asmatidae and suggests a close affinity to Paralellelasma, but 

 Schizostrophina lacks the radial capillae and the characteristic trun- 

 cated margins of the ribs along the commissure of the former genus. 

 Another difference is the parasulcate anterior commissure. 



Schizostrophina margarita Fu, 1982 



PI. 14, figs 2-27; Fig. 20 



1982 Schizostrophina margarita Fu: 132, pi. 37, fig. 5. 

 1982 Schizostrophina shaanxiensis Fu: 133, pi. 37, fig. 6. 



Material. 26 pairs of conjoined valves, 6 ventral and 4 dorsal 

 valves from Samples 100 (=K-98/1970) (BC 57275-7), 626 (BC 

 57279-8 1 ), 8223, Anderkenyn- Akchoku section; Samples 628, 2538 

 (BC 57282-92, 57574-78), 8219 (BC 57294), 8220 (BC 57295), 

 8256 (BC 57296-9), Kujandysai Section. 



Description. Shell equally biconvex, subpentagonal to 

 subtriangular in outline; about as long as wide, with maximum width 

 anterior to mid-valve. Anterior commissure parasulcate. Beaks of 

 both valves swollen and strongly curved. Ventral valve moderately 



Table 28 Measurements of ventral valves of Schizostrophina margarita Fu, Samples 626, 2538, 8256 from Anderkenyn- Akchoku and Kujandysai sections. 





L 



W 



T 



Sw 



St 



LAV 



T/L 



SwAV 



LdAV 



SwAV 



N 



18 



18 



18 



17 



3 



18 



18 



17 



9 



9 



X 



5.8 



6.2 



4.2 



4.3 



4.3 



94.8% 



71.4% 



71.7% 



92.2% 



70.2% 



s 



1.24 



1.68 



1.25 



1.55 



0.92 



6.0 



9.3% 



14.5 



4.9 



5.4 



MIN 



3.6 



3.7 



2.1 



2.6 



3.2 



79.6% 



54.5% 



45.2% 



82.9% 



63.9% 



MAX 



8.0 



9.8 



6.2 



7.8 



4.8 



102.2% 



90.4% 



100.0% 



97.5% 



80.7% 



discrete outer plates 



G) 



1 (0.1) 



2 (<>-2) 3 (0.3) 



4 (0.4) 



5 (0.6) 



6 (0.8) 



5 mm 



5 mm 



Fig. 20 Transverse serial sections of Schizostrophina margarita Fu, Sample 2538, Kujandysai section. Distance in mm is measured from the posterior tip 

 of ventral beak. Dorsal valve uppermost. Also lateral view to show section positions and schematic reconstruction. 



