UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



47 



Table 15 Measurements of complete shells and ventral valves of 

 Anoptambonites convexa sp. nov., Acculina-Dularikarella Association, 

 samples 100 and 626 from Anderkenyn-Akchoku section. 





Lv 



W 



T 



Lv/W 



T/Lv 



N 



18 



17 



8 



17 



8 



X 



12.1 



16.5 



6.9 



71.6% 



47.1% 



s 



4.24 



5.26 



1.86 



7.5 



6.3 



MIN 



5.8 



8.2 



3.5 



57.8% 



39.4% 



MAX 



18.0 



23.9 



9.6 



86.5% 



58.9% 



Table 16 Measurements of complete shells and ventral valves of 



Anoptambonites convexa sp. nov.. Parastrophina-Kelterella Association, 

 samples 2538, 8217 and 8256 from Kujandysai section. 





Lv 



W 



T 



Lv/W 



T/Lv 



N 



11 



11 



4 



11 



4 



X 



6.4 



9.9 



2.8 



65.5% 



44.8% 



s 



1.13 



2.33 



0.57 



7.6 



6.1 



MIN 



5.2 



6.6 



2.0 



57.0% 



38.5% 



MAX 



9.0 



15.3 



3.2 



79.3% 



51.6% 



57461, 63, 65), 8217, 8256 (BC 57070-73), Kujandysai section; 

 Samples 8230 (BC 57069), 8231-40, Buldukbai-Akchoku. 



DESCRIPTION. Shell concavoconvex, transverse, semielliptical in 

 outline, about 72% as long as wide with maximum width at hinge 

 line and thickness 47% of valve length. Cardinal extremities slightly 

 acute to rectangular. Anterior commissure rectimarginate. Ventral 

 valve carinate posteriorly, strongly convex in lateral profile with the 

 maximum thickness at the point of geniculation somewhat anterior 

 to mid-length. Beak pointed and slightly erect posterior to the hinge 



line. Ventral interarea steeply apsacline to procline with mainly open 

 delthyrium covered apically by the minute pseudodeltidium. Dorsal 

 valve gently and unevenly concave in lateral profile, flat to mid- 

 length. A shallow sulcus originates at the umbo and fades towards the 

 anterior margin. Dorsal interarea anacline with convex chilidium. 

 Radial ornament finely and near equally multicostellate with 28^-3 

 primary ribs originating near the umbo and 4—6 ribs per mm at the 

 anterior margin. Concentric ornament of fine, evenly spaced fila. 



Ventral valve with teeth lacking dental plates. Muscle field small, 

 cordate, bisected by fine median ridge separating small, lanceolate 

 adductor scars. Vascula media short, widely diverging. Dorsal inte- 

 rior with undercut cardinal process bearing up to 8 ridges on both 

 sides of strong central lobe. Lophophore platform semielliptical, 

 bordered by a high rim joined to the median septum. Dorsal adductor 

 muscle field subrectangular, about one-third as long as the valve. 



VARIABILITY. The average size of Anoptambonites convexus from 

 the Acculina-Dulankarella Association, which typically occurs 

 within the nodular limestone deposited on the flanks of carbonate 

 mud mounds (Sample 100), is one and half to two times larger than 

 the average size of the shells from the pockets in the mud mound core 

 (Samples 2538 and 8231-40) and the overlying bedded limestone 

 (Samples 628, 8217, 8223, 8256) in which the Parastrophina- 

 Kellereila Association characteristically occurs. However, the 

 specimens from the Parastrophina-KellereUa Association retain a 

 similar outline, transverse and lateral profile of the shells from the 

 Acculina-Dulankarella Association and are also characterized by 

 their multicostellate ornament which consists of 26 to 36 primary 

 ribs and 4 to 6 ribs along the anterior margin of full grown specimens. 



DISCUSSION. This species differs from Anoptambonites grayae 

 (Davidson), as revised by Williams (1962: 1 7 1 ) from the Craighead 



Fig. 12 1-6. Anoptambonites convexus sp. nov. 1, 4, 5, Anderkenyn-Akchoku section, 1, Sample 8223b, BC 57467, ventral exterior, x 3; 4, 5, Sample 100. 

 4, BC 57470, ventral internal mould, x 2; 5, BC 57472. ventral exterior, x 2. 3, 6, Buldukbai section, 3, Sample 8230, BC 57069, ventral internal mould, 

 x 3, 6, Sample 8231, BC 57473, ventral internal mould, x 1.5. 2. Kujandysai section, Sample 8256, ventral exterior, x 2. 



7-14, Sowerbyella (Sowerbyella) aff. ampla (Nikitin & Popov), 7-13, Kujandysai section, Sample 2538, 7, BC 57082, ventral exterior, x 3; 8,9, BC 

 57482, lateral and ventral views of ventral exterior, x 4; 10, BC 57081, ventral internal mould, x 3; 11, 12, BC 57479, anterior and ventral views of 

 ventral exterior, x 3; 13, BC 57481, ventral exterior, x 3. 14, Anderkenyn-Akchoku section. Sample 8214, BC 57480. dorsal exterior, x 2.5. 



