ordovician brachiopoda 139 



Table 104 



Statistics of length (1) and maximum anterior extension of septa (Is) in n brachial valves of 

 5. antiqua Jones from the Ffairfach Group (A), S. cf. antiqua from the Meadowtown Beds (B), 

 S. multiseptata sp. nov. from the Spy Wood Grit (C) and S. cf. sericea permixta Williams from 



the Aldress Shales (D) 





A 



B 



C 



D 



n 



54 



35 



13 



43 



1 mm 



4 -2 



2-98 



273 



4-07 



(var 1) 



(o-599) 



(o-59i) 



(0-424) 



(1-876) 



Is mm 



2-34 



i-8i 



1-98 



2-68 



(var Is) 



(o-i95) 



(0-2) 



(0-305) 



(o-86i) 



r 



0-926 



o-954 



0-915 



0-969 



a 0-5697 0-5817 0-8478 0-6774 



(var a) (0-00088) (0-00092) (0-01065) (0-00068) 



Subfamily AEGIROMENINAE Havlicek 1961 



SERICOIDEA Lindstrom 1953 



Sericoidea cf. abdita Williams 

 (PL 24, figs. 8, 9, 12, 15, 17, 18 ; PL 28, fig. 16) 



1955 Sericoidea abdita Williams : 418. 



Diagnosis. Semicircular Sericoidea with a brachial valve 54% as long as wide 

 and ornamented by unequally developed parvicostellae commonly numbering 11 or 

 12 per mm, 2 mm antero-medially of the dorsal umbo ; median and submedial septa 

 in adult brachial valves extending forwards for about two-thirds the valve length 

 bounded anteriorly by an arc of septules. 



Description. Semicircular, concavo-convex Sericoidea with a concave brachial 

 valve averaging 54% as long as wide in 6 valves (range 50% to 64%) and an evenly 

 convex pedicle valve with a mean depth for 3 valves of 11-3% (range 8-7% to 13-6%) ; 

 ventral and dorsal interareas apsacline and anacline, supra-apical foramen open in 

 adult pedicle valves ; protegulum about 0-2 mm long ; radial ornamentation un- 

 equally parvicostellate with rib frequencies of 11, 12 and 13 per mm, 2 mm antero- 

 medially of the umbones of 3, 3 and 1 brachial valves, divided into sectors about 

 0-5 mm wide by accentuated costae and costellae ; impersistent rugae with a wave- 

 length of about o-i mm occur postero-laterally at acute angles to the hinge-line. 



Ventral interior with unsupported oblique teeth ; subquadrate ventral muscle 

 scar about as wide as long and extending forward for 28% of the length of the pedicle 

 valve, bounded by low subparallel ridges trailing anteriorly from the tooth bases 

 and divided postero-medially by a thin median ridge. 



Dorsal interior with widely splayed socket ridges extending anteriorly for about 

 8% of the length of the valve ; lophophore supports of adult valves consisting of a 

 median septum flanked by a pair of submedial septa extending forward for 62-8% 

 of the length of 6 brachial valves (range 54% to 80%) and a peripheral arc of about 

 8 septules. 



